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 $203.71   6.584%   $217.1223   $217.12   $217.10   $217.10  
  Purchase #2 $126.54   11.290%   $140.8264   $140.83   $140.85   $140.80  
  Purchase #3 $216.91   9.674%   $237.8939   $237.89   $237.90   $237.90  
  Purchase #4 $34.86   9.631%   $38.2174   $38.22   $38.20   $38.20  
  Purchase #5 $158.49   4.750%   $166.0183   $166.02   $166.00   $166.00  
  Purchase #6 $103.90   9.213%   $113.4723   $113.47   $113.45   $113.50  
  Purchase #7 $12.55   7.204%   $13.4541   $13.45   $13.45   $13.50  
  7 purchase totals = $856.96       $927.0047   $927.00   $926.95   $927.00