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 $216.34   13.119%   $244.7216   $244.72   $244.70   $244.70  
  Purchase #2 $151.34   12.840%   $170.7721   $170.77   $170.75   $170.80  
  Purchase #3 $149.76   9.311%   $163.7042   $163.70   $163.70   $163.70  
  Purchase #4 $39.86   8.324%   $43.1779   $43.18   $43.20   $43.20  
  Purchase #5 $194.77   11.148%   $216.483   $216.48   $216.50   $216.50  
  Purchase #6 $125.62   5.824%   $132.9361   $132.94   $132.95   $132.90  
  Purchase #7 $47.69   9.792%   $52.3598   $52.36   $52.35   $52.40  
  7 purchase totals = $925.38       $1,024.1547   $1,024.15   $1,024.15   $1,024.20