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	$109.70	5.123%	$115.3199	$115.32	$115.30	$115.30
Purchase #2	$64.50	11.723%	$72.0613	$72.06	$72.05	$72.10
Purchase #3	$12.93	10.458%	$14.2822	$14.28	$14.30	$14.30
Purchase #4	$34.80	6.723%	$37.1396	$37.14	$37.15	$37.10
Purchase #5	$79.73	11.685%	$89.0465	$89.05	$89.05	$89.00
Purchase #6	$48.64	5.730%	$51.4271	$51.43	$51.45	$51.40
Purchase #7	$104.86	12.809%	$118.2915	$118.29	$118.30	$118.30
7 purchase totals =	$455.16		$497.5681	$497.57	$497.60	$497.50