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	$179.46	5.582%	$189.4775	$189.48	$189.50	$189.50
Purchase #2	$180.38	6.263%	$191.6772	$191.68	$191.70	$191.70
Purchase #3	$110.90	3.187%	$114.4344	$114.43	$114.45	$114.40
Purchase #4	$200.84	12.497%	$225.939	$225.94	$225.95	$225.90
Purchase #5	$194.38	10.414%	$214.6227	$214.62	$214.60	$214.60
Purchase #6	$138.58	5.655%	$146.4167	$146.42	$146.40	$146.40
Purchase #7	$81.41	10.382%	$89.862	$89.86	$89.85	$89.90
7 purchase totals =	$1,085.95		$1,172.4295	$1,172.43	$1,172.45	$1,172.40