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	$18.34	12.578%	$20.6468	$20.65	$20.65	$20.60
Purchase #2	$87.32	13.505%	$99.1126	$99.11	$99.10	$99.10
Purchase #3	$233.86	11.538%	$260.8428	$260.84	$260.85	$260.80
Purchase #4	$204.56	3.283%	$211.2757	$211.28	$211.30	$211.30
Purchase #5	$229.45	6.650%	$244.7084	$244.71	$244.70	$244.70
Purchase #6	$198.31	13.809%	$225.6946	$225.69	$225.70	$225.70
Purchase #7	$78.44	13.764%	$89.2365	$89.24	$89.25	$89.20
7 purchase totals =	$1,050.28		$1,151.5174	$1,151.52	$1,151.55	$1,151.40