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	$17.52	13.171%	$19.8276	$19.83	$19.85	$19.80
Purchase #2	$229.70	9.785%	$252.1761	$252.18	$252.20	$252.20
Purchase #3	$71.40	10.282%	$78.7413	$78.74	$78.75	$78.70
Purchase #4	$245.97	11.847%	$275.1101	$275.11	$275.10	$275.10
Purchase #5	$156.54	6.366%	$166.5053	$166.51	$166.50	$166.50
Purchase #6	$224.47	7.586%	$241.4983	$241.50	$241.50	$241.50
Purchase #7	$97.88	8.167%	$105.8739	$105.87	$105.85	$105.90
7 purchase totals =	$1,043.48		$1,139.7326	$1,139.74	$1,139.75	$1,139.70