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 $78.69   8.255%   $85.1859   $85.19   $85.20   $85.20  
  Purchase #2 $237.83   4.186%   $247.7856   $247.79   $247.80   $247.80  
  Purchase #3 $164.98   6.187%   $175.1873   $175.19   $175.20   $175.20  
  Purchase #4 $95.55   10.827%   $105.8952   $105.90   $105.90   $105.90  
  Purchase #5 $188.98   4.664%   $197.794   $197.79   $197.80   $197.80  
  Purchase #6 $5.66   9.795%   $6.2144   $6.21   $6.20   $6.20  
  Purchase #7 $195.55   4.201%   $203.7651   $203.77   $203.75   $203.80  
  7 purchase totals = $967.24       $1,021.8275   $1,021.84   $1,021.85   $1,021.90