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 $57.98   13.749%   $65.9517   $65.95   $65.95   $66.00  
  Purchase #2 $111.52   11.827%   $124.7095   $124.71   $124.70   $124.70  
  Purchase #3 $215.71   11.373%   $240.2427   $240.24   $240.25   $240.20  
  Purchase #4 $163.55   3.519%   $169.3053   $169.31   $169.30   $169.30  
  Purchase #5 $31.52   8.501%   $34.1995   $34.20   $34.20   $34.20  
  Purchase #6 $223.57   6.645%   $238.4262   $238.43   $238.45   $238.40  
  Purchase #7 $72.68   5.203%   $76.4615   $76.46   $76.45   $76.50  
  7 purchase totals = $876.53       $949.2964   $949.30   $949.30   $949.30