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 $234.53   13.232%   $265.563   $265.56   $265.55   $265.60  
  Purchase #2 $179.58   8.374%   $194.618   $194.62   $194.60   $194.60  
  Purchase #3 $198.69   12.140%   $222.811   $222.81   $222.80   $222.80  
  Purchase #4 $234.63   4.532%   $245.2634   $245.26   $245.25   $245.30  
  Purchase #5 $105.55   5.357%   $111.2043   $111.20   $111.20   $111.20  
  Purchase #6 $67.41   11.145%   $74.9228   $74.92   $74.90   $74.90  
  Purchase #7 $244.93   3.604%   $253.7573   $253.76   $253.75   $253.80  
  7 purchase totals = $1,265.32       $1,368.1398   $1,368.13   $1,368.05   $1,368.20