Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.51   8.776%   $58.206   $58.21   $58.20   $58.20  
  Purchase #2 $245.53   11.715%   $274.2938   $274.29   $274.30   $274.30  
  Purchase #3 $60.38   4.440%   $63.0609   $63.06   $63.05   $63.10  
  Purchase #4 $237.35   12.102%   $266.0741   $266.07   $266.05   $266.10  
  Purchase #5 $106.87   3.196%   $110.2856   $110.29   $110.30   $110.30  
  Purchase #6 $207.93   7.445%   $223.4104   $223.41   $223.40   $223.40  
  Purchase #7 $226.31   12.631%   $254.8952   $254.90   $254.90   $254.90  
  7 purchase totals = $1,137.88       $1,250.2260   $1,250.23   $1,250.20   $1,250.30