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 $54.35   9.723%   $59.6345   $59.63   $59.65   $59.60  
  Purchase #2 $194.48   13.811%   $221.3396   $221.34   $221.35   $221.30  
  Purchase #3 $217.36   8.671%   $236.2073   $236.21   $236.20   $236.20  
  Purchase #4 $175.49   13.826%   $199.7532   $199.75   $199.75   $199.80  
  Purchase #5 $104.43   5.324%   $109.9899   $109.99   $110.00   $110.00  
  Purchase #6 $90.79   12.481%   $102.1215   $102.12   $102.10   $102.10  
  Purchase #7 $158.63   12.647%   $178.6919   $178.69   $178.70   $178.70  
  7 purchase totals = $995.53       $1,107.7379   $1,107.73   $1,107.75   $1,107.70