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	$241.56	4.685%	$252.8771	$252.88	$252.90	$252.90
Purchase #2	$131.70	4.588%	$137.7424	$137.74	$137.75	$137.70
Purchase #3	$82.32	4.286%	$85.8482	$85.85	$85.85	$85.80
Purchase #4	$166.55	11.142%	$185.107	$185.11	$185.10	$185.10
Purchase #5	$227.30	7.456%	$244.2475	$244.25	$244.25	$244.20
Purchase #6	$25.38	13.504%	$28.8073	$28.81	$28.80	$28.80
Purchase #7	$117.94	10.823%	$130.7046	$130.70	$130.70	$130.70
7 purchase totals =	$992.75		$1,065.3341	$1,065.34	$1,065.35	$1,065.20