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 $232.72   5.813%   $246.248   $246.25   $246.25   $246.20  
  Purchase #2 $15.61   12.311%   $17.5317   $17.53   $17.55   $17.50  
  Purchase #3 $242.28   12.186%   $271.8042   $271.80   $271.80   $271.80  
  Purchase #4 $145.73   11.482%   $162.4627   $162.46   $162.45   $162.50  
  Purchase #5 $214.76   4.273%   $223.9367   $223.94   $223.95   $223.90  
  Purchase #6 $183.26   8.652%   $199.1157   $199.12   $199.10   $199.10  
  Purchase #7 $185.33   8.474%   $201.0349   $201.03   $201.05   $201.00  
  7 purchase totals = $1,219.69       $1,322.1339   $1,322.13   $1,322.15   $1,322.00