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	$223.58	6.738%	$238.6448	$238.64	$238.65	$238.60
Purchase #2	$139.52	8.741%	$151.7154	$151.72	$151.70	$151.70
Purchase #3	$183.63	4.656%	$192.1798	$192.18	$192.20	$192.20
Purchase #4	$165.37	13.552%	$187.7809	$187.78	$187.80	$187.80
Purchase #5	$53.65	7.673%	$57.7666	$57.77	$57.75	$57.80
Purchase #6	$135.39	5.764%	$143.1939	$143.19	$143.20	$143.20
Purchase #7	$160.80	11.620%	$179.485	$179.49	$179.50	$179.50
7 purchase totals =	$1,061.94		$1,150.7664	$1,150.77	$1,150.80	$1,150.80