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 $186.79   10.797%   $206.9577   $206.96   $206.95   $207.00  
  Purchase #2 $24.37   8.846%   $26.5258   $26.53   $26.55   $26.50  
  Purchase #3 $206.46   8.151%   $223.2886   $223.29   $223.30   $223.30  
  Purchase #4 $70.99   4.596%   $74.2527   $74.25   $74.25   $74.30  
  Purchase #5 $68.83   9.732%   $75.5285   $75.53   $75.55   $75.50  
  Purchase #6 $115.82   8.692%   $125.8871   $125.89   $125.90   $125.90  
  Purchase #7 $202.94   10.599%   $224.4496   $224.45   $224.45   $224.40  
  7 purchase totals = $876.20       $956.8900   $956.90   $956.95   $956.90