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 $223.66   11.596%   $249.5956   $249.60   $249.60   $249.60  
  Purchase #2 $157.91   11.621%   $176.2607   $176.26   $176.25   $176.30  
  Purchase #3 $48.32   7.478%   $51.9334   $51.93   $51.95   $51.90  
  Purchase #4 $28.98   13.529%   $32.9007   $32.90   $32.90   $32.90  
  Purchase #5 $42.81   12.719%   $48.255   $48.26   $48.25   $48.30  
  Purchase #6 $61.33   3.684%   $63.5894   $63.59   $63.60   $63.60  
  Purchase #7 $222.36   9.816%   $244.1869   $244.19   $244.20   $244.20  
  7 purchase totals = $785.37       $866.7217   $866.73   $866.75   $866.80