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 $185.43   11.267%   $206.3224   $206.32   $206.30   $206.30  
  Purchase #2 $217.98   11.450%   $242.9387   $242.94   $242.95   $242.90  
  Purchase #3 $21.79   6.159%   $23.132   $23.13   $23.15   $23.10  
  Purchase #4 $121.55   12.635%   $136.9078   $136.91   $136.90   $136.90  
  Purchase #5 $103.70   12.444%   $116.6044   $116.60   $116.60   $116.60  
  Purchase #6 $131.63   3.117%   $135.7329   $135.73   $135.75   $135.70  
  Purchase #7 $97.47   8.457%   $105.713   $105.71   $105.70   $105.70  
  7 purchase totals = $879.55       $967.3512   $967.34   $967.35   $967.20