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 $237.98   11.339%   $264.9646   $264.96   $264.95   $265.00  
  Purchase #2 $160.67   5.734%   $169.8828   $169.88   $169.90   $169.90  
  Purchase #3 $103.45   13.849%   $117.7768   $117.78   $117.80   $117.80  
  Purchase #4 $31.95   5.313%   $33.6475   $33.65   $33.65   $33.60  
  Purchase #5 $31.75   11.315%   $35.3425   $35.34   $35.35   $35.30  
  Purchase #6 $67.89   10.102%   $74.7482   $74.75   $74.75   $74.70  
  Purchase #7 $160.34   13.251%   $181.5867   $181.59   $181.60   $181.60  
  7 purchase totals = $794.03       $877.9491   $877.95   $878.00   $877.90