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 $232.45   13.269%   $263.2938   $263.29   $263.30   $263.30  
  Purchase #2 $66.92   5.351%   $70.5009   $70.50   $70.50   $70.50  
  Purchase #3 $215.30   9.281%   $235.282   $235.28   $235.30   $235.30  
  Purchase #4 $214.79   10.238%   $236.7802   $236.78   $236.80   $236.80  
  Purchase #5 $197.63   8.515%   $214.4582   $214.46   $214.45   $214.50  
  Purchase #6 $57.47   4.189%   $59.8774   $59.88   $59.90   $59.90  
  Purchase #7 $182.68   12.233%   $205.0272   $205.03   $205.05   $205.00  
  7 purchase totals = $1,167.24       $1,285.2197   $1,285.22   $1,285.30   $1,285.30