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 $69.31   5.693%   $73.2558   $73.26   $73.25   $73.30  
  Purchase #2 $104.49   4.496%   $109.1879   $109.19   $109.20   $109.20  
  Purchase #3 $137.29   9.859%   $150.8254   $150.83   $150.85   $150.80  
  Purchase #4 $60.45   12.242%   $67.8503   $67.85   $67.85   $67.90  
  Purchase #5 $236.33   10.707%   $261.6339   $261.63   $261.65   $261.60  
  Purchase #6 $235.81   9.831%   $258.9925   $258.99   $259.00   $259.00  
  Purchase #7 $46.99   11.824%   $52.5461   $52.55   $52.55   $52.50  
  7 purchase totals = $890.67       $974.2919   $974.30   $974.35   $974.30