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	$199.95	12.748%	$225.4396	$225.44	$225.45	$225.40
Purchase #2	$111.38	11.791%	$124.5128	$124.51	$124.50	$124.50
Purchase #3	$123.47	6.332%	$131.2881	$131.29	$131.30	$131.30
Purchase #4	$88.47	4.164%	$92.1539	$92.15	$92.15	$92.20
Purchase #5	$79.32	9.640%	$86.9664	$86.97	$86.95	$87.00
Purchase #6	$81.41	9.714%	$89.3182	$89.32	$89.30	$89.30
Purchase #7	$45.95	12.797%	$51.8302	$51.83	$51.85	$51.80
7 purchase totals =	$729.95		$801.5092	$801.51	$801.50	$801.50