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 $48.65   13.310%   $55.1253   $55.13   $55.15   $55.10  
  Purchase #2 $169.71   12.282%   $190.5538   $190.55   $190.55   $190.60  
  Purchase #3 $189.43   5.542%   $199.9282   $199.93   $199.95   $199.90  
  Purchase #4 $106.46   12.288%   $119.5418   $119.54   $119.55   $119.50  
  Purchase #5 $97.94   4.700%   $102.5432   $102.54   $102.55   $102.50  
  Purchase #6 $102.52   11.413%   $114.2206   $114.22   $114.20   $114.20  
  Purchase #7 $182.90   5.795%   $193.4991   $193.50   $193.50   $193.50  
  7 purchase totals = $897.61       $975.4120   $975.41   $975.45   $975.30