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 $234.93   8.252%   $254.3164   $254.32   $254.30   $254.30  
  Purchase #2 $31.35   12.515%   $35.2735   $35.27   $35.25   $35.30  
  Purchase #3 $192.35   3.656%   $199.3823   $199.38   $199.40   $199.40  
  Purchase #4 $18.92   4.839%   $19.8355   $19.84   $19.85   $19.80  
  Purchase #5 $165.50   3.641%   $171.5259   $171.53   $171.55   $171.50  
  Purchase #6 $142.31   5.222%   $149.7414   $149.74   $149.75   $149.70  
  Purchase #7 $192.58   13.278%   $218.1508   $218.15   $218.15   $218.20  
  7 purchase totals = $977.94       $1,048.2258   $1,048.23   $1,048.25   $1,048.20