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	$31.91	4.313%	$33.2863	$33.29	$33.30	$33.30
Purchase #2	$249.77	9.104%	$272.5091	$272.51	$272.50	$272.50
Purchase #3	$115.39	10.515%	$127.5233	$127.52	$127.50	$127.50
Purchase #4	$80.68	3.816%	$83.7587	$83.76	$83.75	$83.80
Purchase #5	$37.36	3.198%	$38.5548	$38.55	$38.55	$38.60
Purchase #6	$34.49	11.580%	$38.4839	$38.48	$38.50	$38.50
Purchase #7	$127.73	8.254%	$138.2728	$138.27	$138.25	$138.30
7 purchase totals =	$677.33		$732.3889	$732.38	$732.35	$732.50