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	$249.91	10.246%	$275.5158	$275.52	$275.50	$275.50
Purchase #2	$119.46	6.334%	$127.0266	$127.03	$127.05	$127.00
Purchase #3	$106.54	8.236%	$115.3146	$115.31	$115.30	$115.30
Purchase #4	$48.57	4.122%	$50.5721	$50.57	$50.55	$50.60
Purchase #5	$184.58	12.679%	$207.9829	$207.98	$208.00	$208.00
Purchase #6	$140.43	8.363%	$152.1742	$152.17	$152.15	$152.20
Purchase #7	$48.53	3.502%	$50.2295	$50.23	$50.25	$50.20
7 purchase totals =	$898.02		$978.8157	$978.81	$978.80	$978.80