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 $217.87   12.419%   $244.9273   $244.93   $244.95   $244.90  
  Purchase #2 $225.31   3.250%   $232.6326   $232.63   $232.65   $232.60  
  Purchase #3 $34.27   8.509%   $37.186   $37.19   $37.20   $37.20  
  Purchase #4 $90.77   4.811%   $95.1369   $95.14   $95.15   $95.10  
  Purchase #5 $125.28   11.668%   $139.8977   $139.90   $139.90   $139.90  
  Purchase #6 $84.88   6.810%   $90.6603   $90.66   $90.65   $90.70  
  Purchase #7 $57.82   12.102%   $64.8174   $64.82   $64.80   $64.80  
  7 purchase totals = $836.20       $905.2582   $905.27   $905.30   $905.20