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	$26.55	5.433%	$27.9925	$27.99	$28.00	$28.00
Purchase #2	$154.46	7.413%	$165.9101	$165.91	$165.90	$165.90
Purchase #3	$222.52	6.705%	$237.44	$237.44	$237.45	$237.40
Purchase #4	$120.72	5.850%	$127.7821	$127.78	$127.80	$127.80
Purchase #5	$28.63	3.437%	$29.614	$29.61	$29.60	$29.60
Purchase #6	$50.56	8.298%	$54.7555	$54.76	$54.75	$54.80
Purchase #7	$111.60	8.119%	$120.6608	$120.66	$120.65	$120.70
7 purchase totals =	$715.04		$764.1550	$764.15	$764.15	$764.20