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 $188.78   5.562%   $199.2799   $199.28   $199.30   $199.30  
  Purchase #2 $68.95   10.148%   $75.947   $75.95   $75.95   $75.90  
  Purchase #3 $86.95   8.438%   $94.2868   $94.29   $94.30   $94.30  
  Purchase #4 $64.38   9.388%   $70.424   $70.42   $70.40   $70.40  
  Purchase #5 $206.76   10.852%   $229.1976   $229.20   $229.20   $229.20  
  Purchase #6 $103.83   8.220%   $112.3648   $112.36   $112.35   $112.40  
  Purchase #7 $210.83   8.761%   $229.3008   $229.30   $229.30   $229.30  
  7 purchase totals = $930.48       $1,010.8009   $1,010.80   $1,010.80   $1,010.80