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 $53.34   12.358%   $59.9318   $59.93   $59.95   $59.90  
  Purchase #2 $239.52   8.429%   $259.7091   $259.71   $259.70   $259.70  
  Purchase #3 $104.84   13.749%   $119.2545   $119.25   $119.25   $119.30  
  Purchase #4 $169.90   13.413%   $192.6887   $192.69   $192.70   $192.70  
  Purchase #5 $190.26   3.698%   $197.2958   $197.30   $197.30   $197.30  
  Purchase #6 $44.82   5.516%   $47.2923   $47.29   $47.30   $47.30  
  Purchase #7 $79.78   6.258%   $84.7726   $84.77   $84.75   $84.80  
  7 purchase totals = $882.46       $960.9448   $960.94   $960.95   $961.00