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	$101.25	13.243%	$114.6585	$114.66	$114.65	$114.70
Purchase #2	$180.57	7.726%	$194.5208	$194.52	$194.50	$194.50
Purchase #3	$131.65	6.150%	$139.7465	$139.75	$139.75	$139.70
Purchase #4	$192.80	6.242%	$204.8346	$204.83	$204.85	$204.80
Purchase #5	$146.62	12.585%	$165.0721	$165.07	$165.05	$165.10
Purchase #6	$64.40	9.442%	$70.4806	$70.48	$70.50	$70.50
Purchase #7	$79.36	12.349%	$89.1602	$89.16	$89.15	$89.20
7 purchase totals =	$896.65		$978.4733	$978.47	$978.45	$978.50