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 $66.56   10.341%   $73.443   $73.44   $73.45   $73.40  
  Purchase #2 $216.29   3.219%   $223.2524   $223.25   $223.25   $223.30  
  Purchase #3 $92.88   8.547%   $100.8185   $100.82   $100.80   $100.80  
  Purchase #4 $69.77   7.185%   $74.783   $74.78   $74.80   $74.80  
  Purchase #5 $197.84   12.178%   $221.933   $221.93   $221.95   $221.90  
  Purchase #6 $27.63   9.231%   $30.1805   $30.18   $30.20   $30.20  
  Purchase #7 $160.88   12.255%   $180.5958   $180.60   $180.60   $180.60  
  7 purchase totals = $831.85       $905.0062   $905.00   $905.05   $905.00