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	$5.94	5.849%	$6.2874	$6.29	$6.30	$6.30
Purchase #2	$84.75	7.823%	$91.38	$91.38	$91.40	$91.40
Purchase #3	$210.37	3.230%	$217.165	$217.17	$217.15	$217.20
Purchase #4	$108.38	11.566%	$120.9152	$120.92	$120.90	$120.90
Purchase #5	$111.48	4.441%	$116.4308	$116.43	$116.45	$116.40
Purchase #6	$90.93	10.767%	$100.7204	$100.72	$100.70	$100.70
Purchase #7	$79.29	3.505%	$82.0691	$82.07	$82.05	$82.10
7 purchase totals =	$691.14		$734.9679	$734.98	$734.95	$735.00