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	$127.27	5.858%	$134.7255	$134.73	$134.75	$134.70
Purchase #2	$55.51	7.778%	$59.8276	$59.83	$59.85	$59.80
Purchase #3	$134.72	3.391%	$139.2884	$139.29	$139.30	$139.30
Purchase #4	$50.28	7.790%	$54.1968	$54.20	$54.20	$54.20
Purchase #5	$72.77	7.223%	$78.0262	$78.03	$78.05	$78.00
Purchase #6	$120.87	11.797%	$135.129	$135.13	$135.15	$135.10
Purchase #7	$19.65	4.240%	$20.4832	$20.48	$20.50	$20.50
7 purchase totals =	$581.07		$621.6767	$621.69	$621.80	$621.60