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 $47.91   9.726%   $52.5697   $52.57   $52.55   $52.60  
  Purchase #2 $241.59   13.354%   $273.8519   $273.85   $273.85   $273.90  
  Purchase #3 $74.96   12.812%   $84.5639   $84.56   $84.55   $84.60  
  Purchase #4 $121.62   6.382%   $129.3818   $129.38   $129.40   $129.40  
  Purchase #5 $138.25   12.699%   $155.8064   $155.81   $155.80   $155.80  
  Purchase #6 $176.82   3.446%   $182.9132   $182.91   $182.90   $182.90  
  Purchase #7 $58.34   11.760%   $65.2008   $65.20   $65.20   $65.20  
  7 purchase totals = $859.49       $944.2877   $944.28   $944.25   $944.40