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 $23.85   12.205%   $26.7609   $26.76   $26.75   $26.80  
  Purchase #2 $152.50   10.853%   $169.0508   $169.05   $169.05   $169.10  
  Purchase #3 $247.75   4.440%   $258.7501   $258.75   $258.75   $258.80  
  Purchase #4 $71.81   7.112%   $76.9171   $76.92   $76.90   $76.90  
  Purchase #5 $23.50   11.788%   $26.2702   $26.27   $26.25   $26.30  
  Purchase #6 $65.27   4.682%   $68.3259   $68.33   $68.35   $68.30  
  Purchase #7 $158.98   7.792%   $171.3677   $171.37   $171.35   $171.40  
  7 purchase totals = $743.66       $797.4427   $797.45   $797.40   $797.60