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	$86.28	4.172%	$89.8796	$89.88	$89.90	$89.90
Purchase #2	$27.47	7.391%	$29.5003	$29.50	$29.50	$29.50
Purchase #3	$104.82	6.658%	$111.7989	$111.80	$111.80	$111.80
Purchase #4	$114.51	8.324%	$124.0418	$124.04	$124.05	$124.00
Purchase #5	$155.33	6.352%	$165.1966	$165.20	$165.20	$165.20
Purchase #6	$97.72	7.622%	$105.1682	$105.17	$105.15	$105.20
Purchase #7	$152.95	5.867%	$161.9236	$161.92	$161.90	$161.90
7 purchase totals =	$739.08		$787.5090	$787.51	$787.50	$787.50