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 $145.79   12.229%   $163.6187   $163.62   $163.60   $163.60  
  Purchase #2 $54.76   10.265%   $60.3811   $60.38   $60.40   $60.40  
  Purchase #3 $48.85   11.829%   $54.6285   $54.63   $54.65   $54.60  
  Purchase #4 $60.94   13.551%   $69.198   $69.20   $69.20   $69.20  
  Purchase #5 $182.46   7.116%   $195.4439   $195.44   $195.45   $195.40  
  Purchase #6 $125.35   5.486%   $132.2267   $132.23   $132.25   $132.20  
  Purchase #7 $82.43   9.217%   $90.0276   $90.03   $90.05   $90.00  
  7 purchase totals = $700.58       $765.5245   $765.53   $765.60   $765.40