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	$183.91	3.572%	$190.4793	$190.48	$190.50	$190.50
Purchase #2	$98.61	7.590%	$106.0945	$106.09	$106.10	$106.10
Purchase #3	$105.42	6.174%	$111.9286	$111.93	$111.95	$111.90
Purchase #4	$47.56	6.111%	$50.4664	$50.47	$50.45	$50.50
Purchase #5	$230.74	5.872%	$244.2891	$244.29	$244.30	$244.30
Purchase #6	$244.34	4.688%	$255.7947	$255.79	$255.80	$255.80
Purchase #7	$193.33	7.369%	$207.5765	$207.58	$207.60	$207.60
7 purchase totals =	$1,103.91		$1,166.6291	$1,166.63	$1,166.70	$1,166.70