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	$90.91	10.152%	$100.1392	$100.14	$100.15	$100.10
Purchase #2	$117.44	6.175%	$124.6919	$124.69	$124.70	$124.70
Purchase #3	$70.45	5.805%	$74.5396	$74.54	$74.55	$74.50
Purchase #4	$24.33	4.428%	$25.4073	$25.41	$25.40	$25.40
Purchase #5	$122.77	13.204%	$138.9806	$138.98	$139.00	$139.00
Purchase #6	$168.68	7.613%	$181.5216	$181.52	$181.50	$181.50
Purchase #7	$39.36	7.362%	$42.2577	$42.26	$42.25	$42.30
7 purchase totals =	$633.94		$687.5379	$687.54	$687.55	$687.50