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 $29.94   9.353%   $32.7403   $32.74   $32.75   $32.70  
  Purchase #2 $180.64   13.704%   $205.3949   $205.39   $205.40   $205.40  
  Purchase #3 $21.50   8.863%   $23.4055   $23.41   $23.40   $23.40  
  Purchase #4 $105.63   6.666%   $112.6713   $112.67   $112.65   $112.70  
  Purchase #5 $24.37   9.321%   $26.6415   $26.64   $26.65   $26.60  
  Purchase #6 $184.33   5.789%   $195.0009   $195.00   $195.00   $195.00  
  Purchase #7 $95.28   3.312%   $98.4357   $98.44   $98.45   $98.40  
  7 purchase totals = $641.69       $694.2901   $694.29   $694.30   $694.20