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	$178.90	4.426%	$186.8181	$186.82	$186.80	$186.80
Purchase #2	$125.51	10.169%	$138.2731	$138.27	$138.25	$138.30
Purchase #3	$245.87	7.584%	$264.5168	$264.52	$264.50	$264.50
Purchase #4	$110.81	11.388%	$123.429	$123.43	$123.45	$123.40
Purchase #5	$161.82	10.358%	$178.5813	$178.58	$178.60	$178.60
Purchase #6	$78.88	13.362%	$89.4199	$89.42	$89.40	$89.40
Purchase #7	$67.64	8.404%	$73.3245	$73.32	$73.30	$73.30
7 purchase totals =	$969.43		$1,054.3627	$1,054.36	$1,054.30	$1,054.30