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	$81.28	9.103%	$88.6789	$88.68	$88.70	$88.70
Purchase #2	$34.82	10.198%	$38.3709	$38.37	$38.35	$38.40
Purchase #3	$239.78	6.841%	$256.1833	$256.18	$256.20	$256.20
Purchase #4	$28.73	4.125%	$29.9151	$29.92	$29.90	$29.90
Purchase #5	$240.70	6.429%	$256.1746	$256.17	$256.15	$256.20
Purchase #6	$245.57	4.550%	$256.7434	$256.74	$256.75	$256.70
Purchase #7	$89.59	4.754%	$93.8491	$93.85	$93.85	$93.80
7 purchase totals =	$960.47		$1,019.9153	$1,019.91	$1,019.90	$1,019.90