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 $187.91   11.127%   $208.8187   $208.82   $208.80   $208.80  
  Purchase #2 $76.78   8.572%   $83.3616   $83.36   $83.35   $83.40  
  Purchase #3 $153.43   3.747%   $159.179   $159.18   $159.20   $159.20  
  Purchase #4 $73.84   4.599%   $77.2359   $77.24   $77.25   $77.20  
  Purchase #5 $222.94   10.824%   $247.071   $247.07   $247.05   $247.10  
  Purchase #6 $192.80   8.541%   $209.267   $209.27   $209.25   $209.30  
  Purchase #7 $243.50   5.676%   $257.3211   $257.32   $257.30   $257.30  
  7 purchase totals = $1,151.20       $1,242.2543   $1,242.26   $1,242.20   $1,242.30