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 $208.73   13.396%   $236.6915   $236.69   $236.70   $236.70  
  Purchase #2 $118.50   5.392%   $124.8895   $124.89   $124.90   $124.90  
  Purchase #3 $173.63   12.266%   $194.9275   $194.93   $194.95   $194.90  
  Purchase #4 $43.95   9.403%   $48.0826   $48.08   $48.10   $48.10  
  Purchase #5 $13.74   4.503%   $14.3587   $14.36   $14.35   $14.40  
  Purchase #6 $12.85   5.852%   $13.602   $13.60   $13.60   $13.60  
  Purchase #7 $197.79   10.659%   $218.8724   $218.87   $218.85   $218.90  
  7 purchase totals = $769.19       $851.4242   $851.42   $851.45   $851.50