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 $225.78   9.522%   $247.2788   $247.28   $247.30   $247.30  
  Purchase #2 $126.98   8.245%   $137.4495   $137.45   $137.45   $137.40  
  Purchase #3 $148.66   9.811%   $163.245   $163.25   $163.25   $163.20  
  Purchase #4 $31.63   13.578%   $35.9247   $35.92   $35.90   $35.90  
  Purchase #5 $247.78   10.291%   $273.279   $273.28   $273.30   $273.30  
  Purchase #6 $169.82   9.764%   $186.4012   $186.40   $186.40   $186.40  
  Purchase #7 $249.54   5.694%   $263.7488   $263.75   $263.75   $263.70  
  7 purchase totals = $1,200.19       $1,307.3270   $1,307.33   $1,307.35   $1,307.20