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 $235.27   8.104%   $254.3363   $254.34   $254.35   $254.30  
  Purchase #2 $134.59   10.345%   $148.5133   $148.51   $148.50   $148.50  
  Purchase #3 $37.95   9.266%   $41.4664   $41.47   $41.45   $41.50  
  Purchase #4 $234.64   10.675%   $259.6878   $259.69   $259.70   $259.70  
  Purchase #5 $154.40   12.161%   $173.1766   $173.18   $173.20   $173.20  
  Purchase #6 $6.42   4.797%   $6.728   $6.73   $6.75   $6.70  
  Purchase #7 $59.89   7.412%   $64.329   $64.33   $64.35   $64.30  
  7 purchase totals = $863.16       $948.2374   $948.25   $948.30   $948.20