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 $67.29   12.116%   $75.4429   $75.44   $75.45   $75.40  
  Purchase #2 $105.63   10.141%   $116.3419   $116.34   $116.35   $116.30  
  Purchase #3 $191.44   6.220%   $203.3476   $203.35   $203.35   $203.30  
  Purchase #4 $202.92   5.168%   $213.4069   $213.41   $213.40   $213.40  
  Purchase #5 $73.76   11.526%   $82.2616   $82.26   $82.25   $82.30  
  Purchase #6 $212.72   13.185%   $240.7671   $240.77   $240.75   $240.80  
  Purchase #7 $11.69   5.185%   $12.2961   $12.30   $12.30   $12.30  
  7 purchase totals = $865.45       $943.8641   $943.87   $943.85   $943.80