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 $67.66   12.341%   $76.0099   $76.01   $76.00   $76.00  
  Purchase #2 $35.97   5.455%   $37.9322   $37.93   $37.95   $37.90  
  Purchase #3 $117.93   13.427%   $133.7645   $133.76   $133.75   $133.80  
  Purchase #4 $167.76   10.395%   $185.1987   $185.20   $185.20   $185.20  
  Purchase #5 $231.48   3.226%   $238.9475   $238.95   $238.95   $238.90  
  Purchase #6 $73.48   7.335%   $78.8698   $78.87   $78.85   $78.90  
  Purchase #7 $5.50   8.523%   $5.9688   $5.97   $5.95   $6.00  
  7 purchase totals = $699.78       $756.6914   $756.69   $756.65   $756.70