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 $41.52   8.213%   $44.93   $44.93   $44.95   $44.90  
  Purchase #2 $217.99   10.408%   $240.6784   $240.68   $240.70   $240.70  
  Purchase #3 $71.38   10.479%   $78.8599   $78.86   $78.85   $78.90  
  Purchase #4 $216.34   13.134%   $244.7541   $244.75   $244.75   $244.80  
  Purchase #5 $168.90   10.686%   $186.9487   $186.95   $186.95   $186.90  
  Purchase #6 $72.99   5.346%   $76.892   $76.89   $76.90   $76.90  
  Purchase #7 $101.61   11.347%   $113.1397   $113.14   $113.15   $113.10  
  7 purchase totals = $890.73       $986.2028   $986.20   $986.25   $986.20