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	$66.72	8.668%	$72.5033	$72.50	$72.50	$72.50
Purchase #2	$104.64	5.209%	$110.0907	$110.09	$110.10	$110.10
Purchase #3	$14.55	4.676%	$15.2304	$15.23	$15.25	$15.20
Purchase #4	$144.61	3.535%	$149.722	$149.72	$149.70	$149.70
Purchase #5	$100.33	4.732%	$105.0776	$105.08	$105.10	$105.10
Purchase #6	$226.41	13.208%	$256.3142	$256.31	$256.30	$256.30
Purchase #7	$45.35	10.466%	$50.0963	$50.10	$50.10	$50.10
7 purchase totals =	$702.61		$759.0345	$759.03	$759.05	$759.00