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 $54.96   9.805%   $60.3488   $60.35   $60.35   $60.30  
  Purchase #2 $216.75   13.505%   $246.0221   $246.02   $246.00   $246.00  
  Purchase #3 $151.36   8.742%   $164.5919   $164.59   $164.60   $164.60  
  Purchase #4 $104.76   9.822%   $115.0495   $115.05   $115.05   $115.00  
  Purchase #5 $54.63   3.488%   $56.5355   $56.54   $56.55   $56.50  
  Purchase #6 $233.27   8.788%   $253.7698   $253.77   $253.75   $253.80  
  Purchase #7 $159.40   7.247%   $170.9517   $170.95   $170.95   $171.00  
  7 purchase totals = $975.13       $1,067.2693   $1,067.27   $1,067.25   $1,067.20