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	$179.64	3.734%	$186.3478	$186.35	$186.35	$186.30
Purchase #2	$142.84	9.848%	$156.9069	$156.91	$156.90	$156.90
Purchase #3	$165.30	3.142%	$170.4937	$170.49	$170.50	$170.50
Purchase #4	$196.49	13.239%	$222.5033	$222.50	$222.50	$222.50
Purchase #5	$144.80	10.313%	$159.7332	$159.73	$159.75	$159.70
Purchase #6	$59.70	9.374%	$65.2963	$65.30	$65.30	$65.30
Purchase #7	$194.54	5.162%	$204.5822	$204.58	$204.60	$204.60
7 purchase totals =	$1,083.31		$1,165.8634	$1,165.86	$1,165.90	$1,165.80