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 $125.66   11.545%   $140.1674   $140.17   $140.15   $140.20  
  Purchase #2 $173.47   11.165%   $192.8379   $192.84   $192.85   $192.80  
  Purchase #3 $113.58   4.621%   $118.8285   $118.83   $118.85   $118.80  
  Purchase #4 $186.39   3.866%   $193.5958   $193.60   $193.60   $193.60  
  Purchase #5 $129.73   3.597%   $134.3964   $134.40   $134.40   $134.40  
  Purchase #6 $101.33   6.187%   $107.5993   $107.60   $107.60   $107.60  
  Purchase #7 $130.45   13.651%   $148.2577   $148.26   $148.25   $148.30  
  7 purchase totals = $960.61       $1,035.6830   $1,035.70   $1,035.70   $1,035.70