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 $206.83   8.283%   $223.9617   $223.96   $223.95   $224.00  
  Purchase #2 $93.83   4.331%   $97.8938   $97.89   $97.90   $97.90  
  Purchase #3 $63.34   11.185%   $70.4246   $70.42   $70.40   $70.40  
  Purchase #4 $232.68   3.525%   $240.882   $240.88   $240.90   $240.90  
  Purchase #5 $31.92   13.363%   $36.1855   $36.19   $36.20   $36.20  
  Purchase #6 $134.90   3.593%   $139.747   $139.75   $139.75   $139.70  
  Purchase #7 $194.29   11.118%   $215.8912   $215.89   $215.90   $215.90  
  7 purchase totals = $957.79       $1,024.9858   $1,024.98   $1,025.00   $1,025.00