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 $214.93   12.734%   $242.2992   $242.30   $242.30   $242.30  
  Purchase #2 $250.76   3.137%   $258.6263   $258.63   $258.65   $258.60  
  Purchase #3 $62.43   5.668%   $65.9685   $65.97   $65.95   $66.00  
  Purchase #4 $13.56   7.676%   $14.6009   $14.60   $14.60   $14.60  
  Purchase #5 $121.96   12.707%   $137.4575   $137.46   $137.45   $137.50  
  Purchase #6 $126.78   4.704%   $132.7437   $132.74   $132.75   $132.70  
  Purchase #7 $64.69   4.604%   $67.6683   $67.67   $67.65   $67.70  
  7 purchase totals = $855.11       $919.3644   $919.37   $919.35   $919.40