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 $183.46   13.788%   $208.7555   $208.76   $208.75   $208.80  
  Purchase #2 $12.70   10.134%   $13.987   $13.99   $14.00   $14.00  
  Purchase #3 $23.67   4.322%   $24.693   $24.69   $24.70   $24.70  
  Purchase #4 $195.47   13.465%   $221.79   $221.79   $221.80   $221.80  
  Purchase #5 $216.62   11.811%   $242.205   $242.21   $242.20   $242.20  
  Purchase #6 $108.42   6.220%   $115.1637   $115.16   $115.15   $115.20  
  Purchase #7 $187.89   3.636%   $194.7217   $194.72   $194.70   $194.70  
  7 purchase totals = $928.23       $1,021.3159   $1,021.32   $1,021.30   $1,021.40