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	$18.56	9.449%	$20.3137	$20.31	$20.30	$20.30
Purchase #2	$92.52	12.481%	$104.0674	$104.07	$104.05	$104.10
Purchase #3	$138.52	5.801%	$146.5555	$146.56	$146.55	$146.60
Purchase #4	$188.66	11.695%	$210.7238	$210.72	$210.70	$210.70
Purchase #5	$118.70	4.581%	$124.1376	$124.14	$124.15	$124.10
Purchase #6	$51.88	9.498%	$56.8076	$56.81	$56.80	$56.80
Purchase #7	$175.83	4.794%	$184.2593	$184.26	$184.25	$184.30
7 purchase totals =	$784.67		$846.8649	$846.87	$846.80	$846.90