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 $224.79   5.771%   $237.7626   $237.76   $237.75   $237.80  
  Purchase #2 $185.50   10.282%   $204.5731   $204.57   $204.55   $204.60  
  Purchase #3 $18.50   8.487%   $20.0701   $20.07   $20.05   $20.10  
  Purchase #4 $53.75   9.283%   $58.7396   $58.74   $58.75   $58.70  
  Purchase #5 $60.76   10.351%   $67.0493   $67.05   $67.05   $67.00  
  Purchase #6 $170.68   12.749%   $192.44   $192.44   $192.45   $192.40  
  Purchase #7 $31.76   10.638%   $35.1386   $35.14   $35.15   $35.10  
  7 purchase totals = $745.74       $815.7733   $815.77   $815.75   $815.70