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 $169.98   5.532%   $179.3833   $179.38   $179.40   $179.40  
  Purchase #2 $241.37   11.291%   $268.6231   $268.62   $268.60   $268.60  
  Purchase #3 $48.40   5.291%   $50.9608   $50.96   $50.95   $51.00  
  Purchase #4 $119.85   13.240%   $135.7181   $135.72   $135.70   $135.70  
  Purchase #5 $12.26   11.786%   $13.705   $13.71   $13.70   $13.70  
  Purchase #6 $118.66   5.484%   $125.1673   $125.17   $125.15   $125.20  
  Purchase #7 $14.86   5.141%   $15.624   $15.62   $15.60   $15.60  
  7 purchase totals = $725.38       $789.1816   $789.18   $789.10   $789.20