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 $67.73   10.622%   $74.9243   $74.92   $74.90   $74.90  
  Purchase #2 $223.49   7.685%   $240.6652   $240.67   $240.65   $240.70  
  Purchase #3 $150.41   5.413%   $158.5517   $158.55   $158.55   $158.60  
  Purchase #4 $33.30   13.408%   $37.7649   $37.76   $37.75   $37.80  
  Purchase #5 $69.99   10.441%   $77.2977   $77.30   $77.30   $77.30  
  Purchase #6 $59.44   5.428%   $62.6664   $62.67   $62.65   $62.70  
  Purchase #7 $231.45   9.533%   $253.5141   $253.51   $253.50   $253.50  
  7 purchase totals = $835.81       $905.3843   $905.38   $905.30   $905.50