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	$10.84	12.788%	$12.2262	$12.23	$12.25	$12.20
Purchase #2	$105.48	11.667%	$117.7864	$117.79	$117.80	$117.80
Purchase #3	$63.83	13.826%	$72.6551	$72.66	$72.65	$72.70
Purchase #4	$72.94	12.573%	$82.1107	$82.11	$82.10	$82.10
Purchase #5	$230.82	4.655%	$241.5647	$241.56	$241.55	$241.60
Purchase #6	$50.79	7.366%	$54.5312	$54.53	$54.55	$54.50
Purchase #7	$184.94	7.725%	$199.2266	$199.23	$199.25	$199.20
7 purchase totals =	$719.64		$780.1009	$780.11	$780.15	$780.10