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 $58.34   12.277%   $65.5024   $65.50   $65.50   $65.50  
  Purchase #2 $65.77   3.684%   $68.193   $68.19   $68.20   $68.20  
  Purchase #3 $143.75   9.354%   $157.1964   $157.20   $157.20   $157.20  
  Purchase #4 $171.34   10.291%   $188.9726   $188.97   $188.95   $189.00  
  Purchase #5 $55.33   7.658%   $59.5672   $59.57   $59.55   $59.60  
  Purchase #6 $146.31   11.344%   $162.9074   $162.91   $162.90   $162.90  
  Purchase #7 $197.77   9.822%   $217.195   $217.20   $217.20   $217.20  
  7 purchase totals = $838.61       $919.5340   $919.54   $919.50   $919.60