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	$117.46	3.152%	$121.1623	$121.16	$121.15	$121.20
Purchase #2	$55.84	9.457%	$61.1208	$61.12	$61.10	$61.10
Purchase #3	$106.73	4.364%	$111.3877	$111.39	$111.40	$111.40
Purchase #4	$52.29	5.737%	$55.2899	$55.29	$55.30	$55.30
Purchase #5	$124.65	7.632%	$134.1633	$134.16	$134.15	$134.20
Purchase #6	$121.97	10.582%	$134.8769	$134.88	$134.90	$134.90
Purchase #7	$46.49	6.422%	$49.4756	$49.48	$49.50	$49.50
7 purchase totals =	$625.43		$667.4765	$667.48	$667.50	$667.60