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 $93.73   7.227%   $100.5039   $100.50   $100.50   $100.50  
  Purchase #2 $189.49   7.105%   $202.9533   $202.95   $202.95   $203.00  
  Purchase #3 $16.53   7.645%   $17.7937   $17.79   $17.80   $17.80  
  Purchase #4 $13.99   8.398%   $15.1649   $15.16   $15.15   $15.20  
  Purchase #5 $50.97   10.223%   $56.1807   $56.18   $56.20   $56.20  
  Purchase #6 $85.44   3.330%   $88.2852   $88.29   $88.30   $88.30  
  Purchase #7 $213.95   5.505%   $225.7279   $225.73   $225.75   $225.70  
  7 purchase totals = $664.10       $706.6096   $706.60   $706.65   $706.70