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 $207.26   8.357%   $224.5807   $224.58   $224.60   $224.60  
  Purchase #2 $125.41   4.117%   $130.5731   $130.57   $130.55   $130.60  
  Purchase #3 $190.76   5.202%   $200.6833   $200.68   $200.70   $200.70  
  Purchase #4 $99.87   12.258%   $112.1121   $112.11   $112.10   $112.10  
  Purchase #5 $69.41   7.439%   $74.5734   $74.57   $74.55   $74.60  
  Purchase #6 $119.93   10.662%   $132.7169   $132.72   $132.70   $132.70  
  Purchase #7 $65.58   13.620%   $74.512   $74.51   $74.50   $74.50  
  7 purchase totals = $878.22       $949.7515   $949.74   $949.70   $949.80