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	$54.56	9.424%	$59.7017	$59.70	$59.70	$59.70
Purchase #2	$7.89	4.601%	$8.253	$8.25	$8.25	$8.30
Purchase #3	$151.48	5.146%	$159.2752	$159.28	$159.30	$159.30
Purchase #4	$127.80	12.728%	$144.0664	$144.07	$144.05	$144.10
Purchase #5	$29.73	4.805%	$31.1585	$31.16	$31.15	$31.20
Purchase #6	$159.71	3.369%	$165.0906	$165.09	$165.10	$165.10
Purchase #7	$16.35	12.643%	$18.4171	$18.42	$18.40	$18.40
7 purchase totals =	$547.52		$585.9625	$585.97	$585.95	$586.10