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	$34.43	9.786%	$37.7993	$37.80	$37.80	$37.80
Purchase #2	$12.55	8.389%	$13.6028	$13.60	$13.60	$13.60
Purchase #3	$157.72	9.345%	$172.4589	$172.46	$172.45	$172.50
Purchase #4	$155.83	11.816%	$174.2429	$174.24	$174.25	$174.20
Purchase #5	$101.66	10.115%	$111.9429	$111.94	$111.95	$111.90
Purchase #6	$92.93	6.754%	$99.2065	$99.21	$99.20	$99.20
Purchase #7	$122.51	13.629%	$139.2069	$139.21	$139.20	$139.20
7 purchase totals =	$677.63		$748.4602	$748.46	$748.45	$748.40