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	$120.49	6.113%	$127.8556	$127.86	$127.85	$127.90
Purchase #2	$157.93	12.863%	$178.2445	$178.24	$178.25	$178.20
Purchase #3	$37.44	13.485%	$42.4888	$42.49	$42.50	$42.50
Purchase #4	$38.76	6.330%	$41.2135	$41.21	$41.20	$41.20
Purchase #5	$74.29	12.848%	$83.8348	$83.83	$83.85	$83.80
Purchase #6	$5.44	7.655%	$5.8564	$5.86	$5.85	$5.90
Purchase #7	$32.41	7.278%	$34.7688	$34.77	$34.75	$34.80
7 purchase totals =	$466.76		$514.2624	$514.26	$514.25	$514.30