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 $73.68   13.334%   $83.5045   $83.50   $83.50   $83.50  
  Purchase #2 $54.96   8.489%   $59.6256   $59.63   $59.65   $59.60  
  Purchase #3 $227.97   7.516%   $245.1042   $245.10   $245.10   $245.10  
  Purchase #4 $9.40   13.274%   $10.6478   $10.65   $10.65   $10.60  
  Purchase #5 $223.93   8.178%   $242.243   $242.24   $242.25   $242.20  
  Purchase #6 $133.86   10.594%   $148.0411   $148.04   $148.05   $148.00  
  Purchase #7 $162.79   8.422%   $176.5002   $176.50   $176.50   $176.50  
  7 purchase totals = $886.59       $965.6664   $965.66   $965.70   $965.50