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 $67.25   9.221%   $73.4511   $73.45   $73.45   $73.50  
  Purchase #2 $83.39   9.189%   $91.0527   $91.05   $91.05   $91.10  
  Purchase #3 $101.69   5.636%   $107.4212   $107.42   $107.40   $107.40  
  Purchase #4 $9.67   11.277%   $10.7605   $10.76   $10.75   $10.80  
  Purchase #5 $94.49   13.375%   $107.128   $107.13   $107.15   $107.10  
  Purchase #6 $93.39   9.814%   $102.5553   $102.56   $102.55   $102.60  
  Purchase #7 $76.54   7.672%   $82.4121   $82.41   $82.40   $82.40  
  7 purchase totals = $526.42       $574.7809   $574.78   $574.75   $574.90