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 $66.49   13.569%   $75.512   $75.51   $75.50   $75.50  
  Purchase #2 $141.62   11.839%   $158.3864   $158.39   $158.40   $158.40  
  Purchase #3 $54.79   11.160%   $60.9046   $60.90   $60.90   $60.90  
  Purchase #4 $195.86   13.192%   $221.6979   $221.70   $221.70   $221.70  
  Purchase #5 $235.35   4.791%   $246.6256   $246.63   $246.65   $246.60  
  Purchase #6 $27.81   8.187%   $30.0868   $30.09   $30.10   $30.10  
  Purchase #7 $124.41   7.257%   $133.4384   $133.44   $133.45   $133.40  
  7 purchase totals = $846.33       $926.6517   $926.66   $926.70   $926.60