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 $195.81   8.483%   $212.4206   $212.42   $212.40   $212.40  
  Purchase #2 $14.61   8.785%   $15.8935   $15.89   $15.90   $15.90  
  Purchase #3 $56.69   12.182%   $63.596   $63.60   $63.60   $63.60  
  Purchase #4 $14.32   3.822%   $14.8673   $14.87   $14.85   $14.90  
  Purchase #5 $142.34   7.668%   $153.2546   $153.25   $153.25   $153.30  
  Purchase #6 $231.41   7.851%   $249.578   $249.58   $249.60   $249.60  
  Purchase #7 $234.83   6.729%   $250.6317   $250.63   $250.65   $250.60  
  7 purchase totals = $890.01       $960.2417   $960.24   $960.25   $960.30