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 $169.63   7.564%   $182.4608   $182.46   $182.45   $182.50  
  Purchase #2 $187.84   10.167%   $206.9377   $206.94   $206.95   $206.90  
  Purchase #3 $98.41   12.837%   $111.0429   $111.04   $111.05   $111.00  
  Purchase #4 $167.92   7.314%   $180.2017   $180.20   $180.20   $180.20  
  Purchase #5 $104.90   11.195%   $116.6436   $116.64   $116.65   $116.60  
  Purchase #6 $44.35   4.324%   $46.2677   $46.27   $46.25   $46.30  
  Purchase #7 $149.73   9.712%   $164.2718   $164.27   $164.25   $164.30  
  7 purchase totals = $922.78       $1,007.8262   $1,007.82   $1,007.80   $1,007.80