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 $151.79   10.140%   $167.1815   $167.18   $167.20   $167.20  
  Purchase #2 $170.96   13.760%   $194.4841   $194.48   $194.50   $194.50  
  Purchase #3 $101.80   11.595%   $113.6037   $113.60   $113.60   $113.60  
  Purchase #4 $58.36   13.822%   $66.4265   $66.43   $66.45   $66.40  
  Purchase #5 $183.91   9.600%   $201.5654   $201.57   $201.55   $201.60  
  Purchase #6 $164.38   3.258%   $169.7355   $169.74   $169.75   $169.70  
  Purchase #7 $49.71   9.318%   $54.342   $54.34   $54.35   $54.30  
  7 purchase totals = $880.91       $967.3387   $967.34   $967.40   $967.30