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	$93.76	5.745%	$99.1465	$99.15	$99.15	$99.10
Purchase #2	$155.98	7.128%	$167.0983	$167.10	$167.10	$167.10
Purchase #3	$58.54	13.549%	$66.4716	$66.47	$66.45	$66.50
Purchase #4	$233.36	11.717%	$260.7028	$260.70	$260.70	$260.70
Purchase #5	$36.86	12.862%	$41.6009	$41.60	$41.60	$41.60
Purchase #6	$107.85	10.419%	$119.0869	$119.09	$119.10	$119.10
Purchase #7	$134.47	6.557%	$143.2872	$143.29	$143.30	$143.30
7 purchase totals =	$820.82		$897.3942	$897.40	$897.40	$897.40