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 $205.25   12.482%   $230.8693   $230.87   $230.85   $230.90  
  Purchase #2 $117.79   6.423%   $125.3557   $125.36   $125.35   $125.40  
  Purchase #3 $95.86   11.370%   $106.7593   $106.76   $106.75   $106.80  
  Purchase #4 $218.28   11.825%   $244.0916   $244.09   $244.10   $244.10  
  Purchase #5 $27.41   8.773%   $29.8147   $29.81   $29.80   $29.80  
  Purchase #6 $222.93   8.543%   $241.9749   $241.97   $241.95   $242.00  
  Purchase #7 $60.64   10.396%   $66.9441   $66.94   $66.95   $66.90  
  7 purchase totals = $948.16       $1,045.8096   $1,045.80   $1,045.75   $1,045.90