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 $47.65   13.352%   $54.0122   $54.01   $54.00   $54.00  
  Purchase #2 $232.35   12.345%   $261.0336   $261.03   $261.05   $261.00  
  Purchase #3 $150.84   12.662%   $169.9394   $169.94   $169.95   $169.90  
  Purchase #4 $181.46   10.146%   $199.8709   $199.87   $199.85   $199.90  
  Purchase #5 $33.65   5.812%   $35.6057   $35.61   $35.60   $35.60  
  Purchase #6 $92.76   9.404%   $101.4832   $101.48   $101.50   $101.50  
  Purchase #7 $119.29   4.637%   $124.8215   $124.82   $124.80   $124.80  
  7 purchase totals = $858.00       $946.7665   $946.76   $946.75   $946.70