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 $216.49   11.388%   $241.1439   $241.14   $241.15   $241.10  
  Purchase #2 $222.58   7.658%   $239.6252   $239.63   $239.65   $239.60  
  Purchase #3 $208.37   13.338%   $236.1624   $236.16   $236.15   $236.20  
  Purchase #4 $233.84   12.847%   $263.8814   $263.88   $263.90   $263.90  
  Purchase #5 $185.59   6.324%   $197.3267   $197.33   $197.35   $197.30  
  Purchase #6 $27.58   3.264%   $28.4802   $28.48   $28.50   $28.50  
  Purchase #7 $50.67   11.738%   $56.6176   $56.62   $56.60   $56.60  
  7 purchase totals = $1,145.12       $1,263.2374   $1,263.24   $1,263.30   $1,263.20