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 $32.88   9.360%   $35.9576   $35.96   $35.95   $36.00  
  Purchase #2 $102.91   12.477%   $115.7501   $115.75   $115.75   $115.80  
  Purchase #3 $209.72   3.176%   $216.3807   $216.38   $216.40   $216.40  
  Purchase #4 $44.74   12.330%   $50.2564   $50.26   $50.25   $50.30  
  Purchase #5 $201.65   9.406%   $220.6172   $220.62   $220.60   $220.60  
  Purchase #6 $234.85   12.527%   $264.2697   $264.27   $264.25   $264.30  
  Purchase #7 $54.56   11.342%   $60.7482   $60.75   $60.75   $60.70  
  7 purchase totals = $881.31       $963.9799   $963.99   $963.95   $964.10