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 $76.94   9.166%   $83.9923   $83.99   $84.00   $84.00  
  Purchase #2 $145.68   4.832%   $152.7193   $152.72   $152.70   $152.70  
  Purchase #3 $82.63   11.365%   $92.0209   $92.02   $92.00   $92.00  
  Purchase #4 $44.83   8.159%   $48.4877   $48.49   $48.50   $48.50  
  Purchase #5 $47.88   8.251%   $51.8306   $51.83   $51.85   $51.80  
  Purchase #6 $64.76   4.583%   $67.728   $67.73   $67.75   $67.70  
  Purchase #7 $212.54   13.770%   $241.8068   $241.81   $241.80   $241.80  
  7 purchase totals = $675.26       $738.5856   $738.59   $738.60   $738.50