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 $162.68   13.648%   $184.8826   $184.88   $184.90   $184.90  
  Purchase #2 $199.64   5.706%   $211.0315   $211.03   $211.05   $211.00  
  Purchase #3 $151.59   3.179%   $156.409   $156.41   $156.40   $156.40  
  Purchase #4 $84.99   11.321%   $94.6117   $94.61   $94.60   $94.60  
  Purchase #5 $231.32   11.183%   $257.1885   $257.19   $257.20   $257.20  
  Purchase #6 $245.37   4.296%   $255.9111   $255.91   $255.90   $255.90  
  Purchase #7 $134.76   13.785%   $153.3367   $153.34   $153.35   $153.30  
  7 purchase totals = $1,210.35       $1,313.3711   $1,313.37   $1,313.40   $1,313.30