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	$16.40	4.642%	$17.1613	$17.16	$17.15	$17.20
Purchase #2	$17.40	12.212%	$19.5249	$19.52	$19.50	$19.50
Purchase #3	$86.25	3.509%	$89.2765	$89.28	$89.30	$89.30
Purchase #4	$169.70	11.257%	$188.8031	$188.80	$188.80	$188.80
Purchase #5	$111.33	3.390%	$115.1041	$115.10	$115.10	$115.10
Purchase #6	$140.96	13.383%	$159.8247	$159.82	$159.80	$159.80
Purchase #7	$247.82	6.842%	$264.7758	$264.78	$264.80	$264.80
7 purchase totals =	$789.86		$854.4704	$854.46	$854.45	$854.50