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 $85.38   10.461%   $94.3116   $94.31   $94.30   $94.30  
  Purchase #2 $24.77   4.804%   $25.96   $25.96   $25.95   $26.00  
  Purchase #3 $206.57   9.584%   $226.3677   $226.37   $226.35   $226.40  
  Purchase #4 $135.75   3.104%   $139.9637   $139.96   $139.95   $140.00  
  Purchase #5 $181.95   5.238%   $191.4805   $191.48   $191.50   $191.50  
  Purchase #6 $108.56   9.189%   $118.5356   $118.54   $118.55   $118.50  
  Purchase #7 $150.52   5.294%   $158.4885   $158.49   $158.50   $158.50  
  7 purchase totals = $893.50       $955.1076   $955.11   $955.10   $955.20