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 $68.99   8.828%   $75.0804   $75.08   $75.10   $75.10  
  Purchase #2 $83.90   10.842%   $92.9964   $93.00   $93.00   $93.00  
  Purchase #3 $169.95   4.316%   $177.285   $177.29   $177.30   $177.30  
  Purchase #4 $132.49   7.428%   $142.3314   $142.33   $142.35   $142.30  
  Purchase #5 $198.81   13.326%   $225.3034   $225.30   $225.30   $225.30  
  Purchase #6 $125.34   13.779%   $142.6106   $142.61   $142.60   $142.60  
  Purchase #7 $61.56   9.395%   $67.3436   $67.34   $67.35   $67.30  
  7 purchase totals = $841.04       $922.9508   $922.95   $923.00   $922.90