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	$248.43	12.418%	$279.28	$279.28	$279.30	$279.30
Purchase #2	$140.87	8.144%	$152.3425	$152.34	$152.35	$152.30
Purchase #3	$112.47	4.236%	$117.2342	$117.23	$117.25	$117.20
Purchase #4	$158.95	8.714%	$172.8009	$172.80	$172.80	$172.80
Purchase #5	$250.91	9.653%	$275.1303	$275.13	$275.15	$275.10
Purchase #6	$204.92	13.466%	$232.5145	$232.51	$232.50	$232.50
Purchase #7	$36.55	10.767%	$40.4853	$40.49	$40.50	$40.50
7 purchase totals =	$1,153.10		$1,269.7877	$1,269.78	$1,269.85	$1,269.70