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	$170.30	5.233%	$179.2118	$179.21	$179.20	$179.20
Purchase #2	$20.44	3.590%	$21.1738	$21.17	$21.15	$21.20
Purchase #3	$116.50	12.261%	$130.7841	$130.78	$130.80	$130.80
Purchase #4	$40.27	5.117%	$42.3306	$42.33	$42.35	$42.30
Purchase #5	$12.62	7.333%	$13.5454	$13.55	$13.55	$13.50
Purchase #6	$73.37	6.122%	$77.8617	$77.86	$77.85	$77.90
Purchase #7	$246.82	10.683%	$273.1878	$273.19	$273.20	$273.20
7 purchase totals =	$680.32		$738.0952	$738.09	$738.10	$738.10