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 $180.30   12.555%   $202.9367   $202.94   $202.95   $202.90  
  Purchase #2 $246.31   6.216%   $261.6206   $261.62   $261.60   $261.60  
  Purchase #3 $163.49   3.295%   $168.877   $168.88   $168.90   $168.90  
  Purchase #4 $221.94   9.285%   $242.5471   $242.55   $242.55   $242.50  
  Purchase #5 $228.42   5.120%   $240.1151   $240.12   $240.10   $240.10  
  Purchase #6 $66.32   7.364%   $71.2038   $71.20   $71.20   $71.20  
  Purchase #7 $185.50   5.209%   $195.1627   $195.16   $195.15   $195.20  
  7 purchase totals = $1,292.28       $1,382.4630   $1,382.47   $1,382.45   $1,382.40