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	$79.35	12.381%	$89.1743	$89.17	$89.15	$89.20
Purchase #2	$6.93	6.525%	$7.3822	$7.38	$7.40	$7.40
Purchase #3	$84.74	11.847%	$94.7791	$94.78	$94.80	$94.80
Purchase #4	$91.75	4.376%	$95.765	$95.77	$95.75	$95.80
Purchase #5	$60.72	4.731%	$63.5927	$63.59	$63.60	$63.60
Purchase #6	$18.64	12.553%	$20.9799	$20.98	$21.00	$21.00
Purchase #7	$193.43	12.628%	$217.8563	$217.86	$217.85	$217.90
7 purchase totals =	$535.56		$589.5295	$589.53	$589.55	$589.70