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 $241.28   11.219%   $268.3492   $268.35   $268.35   $268.30  
  Purchase #2 $133.72   4.277%   $139.4392   $139.44   $139.45   $139.40  
  Purchase #3 $158.35   3.303%   $163.5803   $163.58   $163.60   $163.60  
  Purchase #4 $212.82   5.598%   $224.7337   $224.73   $224.75   $224.70  
  Purchase #5 $231.86   4.534%   $242.3725   $242.37   $242.35   $242.40  
  Purchase #6 $66.30   6.609%   $70.6818   $70.68   $70.70   $70.70  
  Purchase #7 $211.60   10.140%   $233.0562   $233.06   $233.05   $233.10  
  7 purchase totals = $1,255.93       $1,342.2129   $1,342.21   $1,342.25   $1,342.20