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 $76.81   13.686%   $87.3222   $87.32   $87.30   $87.30  
  Purchase #2 $119.90   4.856%   $125.7223   $125.72   $125.70   $125.70  
  Purchase #3 $114.26   13.849%   $130.0839   $130.08   $130.10   $130.10  
  Purchase #4 $38.39   7.736%   $41.3599   $41.36   $41.35   $41.40  
  Purchase #5 $135.69   6.655%   $144.7202   $144.72   $144.70   $144.70  
  Purchase #6 $246.56   4.254%   $257.0487   $257.05   $257.05   $257.00  
  Purchase #7 $151.64   12.111%   $170.0051   $170.01   $170.00   $170.00  
  7 purchase totals = $883.25       $956.2623   $956.26   $956.20   $956.20