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 $170.45   6.811%   $182.0593   $182.06   $182.05   $182.10  
  Purchase #2 $197.71   13.676%   $224.7488   $224.75   $224.75   $224.70  
  Purchase #3 $232.67   3.469%   $240.7413   $240.74   $240.75   $240.70  
  Purchase #4 $118.91   6.182%   $126.261   $126.26   $126.25   $126.30  
  Purchase #5 $97.66   8.726%   $106.1818   $106.18   $106.20   $106.20  
  Purchase #6 $26.82   13.161%   $30.3498   $30.35   $30.35   $30.30  
  Purchase #7 $39.27   4.589%   $41.0721   $41.07   $41.05   $41.10  
  7 purchase totals = $883.49       $951.4141   $951.41   $951.40   $951.40