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 $232.26   12.178%   $260.5446   $260.54   $260.55   $260.50  
  Purchase #2 $39.44   13.744%   $44.8606   $44.86   $44.85   $44.90  
  Purchase #3 $10.77   13.719%   $12.2475   $12.25   $12.25   $12.20  
  Purchase #4 $62.56   3.581%   $64.8003   $64.80   $64.80   $64.80  
  Purchase #5 $40.62   3.159%   $41.9032   $41.90   $41.90   $41.90  
  Purchase #6 $167.49   5.833%   $177.2597   $177.26   $177.25   $177.30  
  Purchase #7 $110.79   12.735%   $124.8991   $124.90   $124.90   $124.90  
  7 purchase totals = $663.93       $726.5150   $726.51   $726.50   $726.50