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 $59.83   12.306%   $67.1927   $67.19   $67.20   $67.20  
  Purchase #2 $232.84   11.816%   $260.3524   $260.35   $260.35   $260.40  
  Purchase #3 $176.38   10.528%   $194.9493   $194.95   $194.95   $194.90  
  Purchase #4 $41.55   8.215%   $44.9633   $44.96   $44.95   $45.00  
  Purchase #5 $233.66   4.542%   $244.2728   $244.27   $244.25   $244.30  
  Purchase #6 $217.56   11.240%   $242.0137   $242.01   $242.00   $242.00  
  Purchase #7 $189.69   12.358%   $213.1319   $213.13   $213.15   $213.10  
  7 purchase totals = $1,151.51       $1,266.8761   $1,266.86   $1,266.85   $1,266.90