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 $48.41   10.430%   $53.4592   $53.46   $53.45   $53.50  
  Purchase #2 $44.34   5.642%   $46.8417   $46.84   $46.85   $46.80  
  Purchase #3 $124.50   6.428%   $132.5029   $132.50   $132.50   $132.50  
  Purchase #4 $55.90   13.284%   $63.3258   $63.33   $63.35   $63.30  
  Purchase #5 $159.54   6.167%   $169.3788   $169.38   $169.40   $169.40  
  Purchase #6 $186.30   10.649%   $206.1391   $206.14   $206.15   $206.10  
  Purchase #7 $214.75   12.226%   $241.0053   $241.01   $241.00   $241.00  
  7 purchase totals = $833.74       $912.6528   $912.66   $912.70   $912.60