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 $231.76   5.645%   $244.8429   $244.84   $244.85   $244.80  
  Purchase #2 $240.48   4.490%   $251.2776   $251.28   $251.30   $251.30  
  Purchase #3 $47.27   8.386%   $51.2341   $51.23   $51.25   $51.20  
  Purchase #4 $63.58   11.514%   $70.9006   $70.90   $70.90   $70.90  
  Purchase #5 $229.92   10.310%   $253.6248   $253.62   $253.60   $253.60  
  Purchase #6 $72.59   13.594%   $82.4579   $82.46   $82.45   $82.50  
  Purchase #7 $68.87   11.246%   $76.6151   $76.62   $76.60   $76.60  
  7 purchase totals = $954.47       $1,030.9530   $1,030.95   $1,030.95   $1,030.90