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	$18.96	12.629%	$21.3545	$21.35	$21.35	$21.40
Purchase #2	$98.83	10.749%	$109.4532	$109.45	$109.45	$109.50
Purchase #3	$218.26	13.165%	$246.9939	$246.99	$247.00	$247.00
Purchase #4	$237.57	3.708%	$246.3791	$246.38	$246.40	$246.40
Purchase #5	$77.84	9.870%	$85.5228	$85.52	$85.50	$85.50
Purchase #6	$245.89	11.277%	$273.619	$273.62	$273.60	$273.60
Purchase #7	$178.48	12.365%	$200.5491	$200.55	$200.55	$200.50
7 purchase totals =	$1,075.83		$1,183.8716	$1,183.86	$1,183.85	$1,183.90