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 $101.47   9.180%   $110.7849   $110.78   $110.80   $110.80  
  Purchase #2 $103.63   3.472%   $107.228   $107.23   $107.25   $107.20  
  Purchase #3 $42.87   4.632%   $44.8557   $44.86   $44.85   $44.90  
  Purchase #4 $30.89   6.729%   $32.9686   $32.97   $32.95   $33.00  
  Purchase #5 $62.33   10.586%   $68.9283   $68.93   $68.95   $68.90  
  Purchase #6 $31.62   9.151%   $34.5135   $34.51   $34.50   $34.50  
  Purchase #7 $8.89   13.733%   $10.1109   $10.11   $10.10   $10.10  
  7 purchase totals = $381.70       $409.3899   $409.39   $409.40   $409.40