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	$78.57	13.266%	$88.9931	$88.99	$89.00	$89.00
Purchase #2	$111.72	4.111%	$116.3128	$116.31	$116.30	$116.30
Purchase #3	$225.76	13.550%	$256.3505	$256.35	$256.35	$256.40
Purchase #4	$216.34	10.341%	$238.7117	$238.71	$238.70	$238.70
Purchase #5	$248.97	10.595%	$275.3484	$275.35	$275.35	$275.30
Purchase #6	$113.43	4.532%	$118.5706	$118.57	$118.55	$118.60
Purchase #7	$74.78	5.683%	$79.0297	$79.03	$79.05	$79.00
7 purchase totals =	$1,069.57		$1,173.3168	$1,173.31	$1,173.30	$1,173.30