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	$169.50	6.448%	$180.4294	$180.43	$180.45	$180.40
Purchase #2	$111.86	13.687%	$127.1703	$127.17	$127.15	$127.20
Purchase #3	$50.50	11.628%	$56.3721	$56.37	$56.35	$56.40
Purchase #4	$73.76	11.385%	$82.1576	$82.16	$82.15	$82.20
Purchase #5	$92.72	5.139%	$97.4849	$97.48	$97.50	$97.50
Purchase #6	$73.60	7.639%	$79.2223	$79.22	$79.20	$79.20
Purchase #7	$150.84	13.179%	$170.7192	$170.72	$170.70	$170.70
7 purchase totals =	$722.78		$793.5558	$793.55	$793.50	$793.60