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 $224.99   11.375%   $250.5826   $250.58   $250.60   $250.60  
  Purchase #2 $110.63   6.332%   $117.6351   $117.64   $117.65   $117.60  
  Purchase #3 $211.77   7.544%   $227.7459   $227.75   $227.75   $227.70  
  Purchase #4 $121.43   7.256%   $130.241   $130.24   $130.25   $130.20  
  Purchase #5 $213.30   4.664%   $223.2483   $223.25   $223.25   $223.20  
  Purchase #6 $209.37   11.692%   $233.8495   $233.85   $233.85   $233.80  
  Purchase #7 $250.45   10.783%   $277.456   $277.46   $277.45   $277.50  
  7 purchase totals = $1,341.94       $1,460.7584   $1,460.77   $1,460.80   $1,460.60