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	$70.66	5.151%	$74.2997	$74.30	$74.30	$74.30
Purchase #2	$153.41	13.232%	$173.7092	$173.71	$173.70	$173.70
Purchase #3	$199.48	5.764%	$210.978	$210.98	$211.00	$211.00
Purchase #4	$17.34	12.613%	$19.5271	$19.53	$19.55	$19.50
Purchase #5	$44.53	13.426%	$50.5086	$50.51	$50.50	$50.50
Purchase #6	$84.94	5.169%	$89.3305	$89.33	$89.35	$89.30
Purchase #7	$145.41	4.870%	$152.4915	$152.49	$152.50	$152.50
7 purchase totals =	$715.77		$770.8446	$770.85	$770.90	$770.80