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	$161.44	5.608%	$170.4936	$170.49	$170.50	$170.50
Purchase #2	$199.53	10.772%	$221.0234	$221.02	$221.00	$221.00
Purchase #3	$145.51	13.861%	$165.6791	$165.68	$165.70	$165.70
Purchase #4	$83.55	6.384%	$88.8838	$88.88	$88.90	$88.90
Purchase #5	$30.71	6.342%	$32.6576	$32.66	$32.65	$32.70
Purchase #6	$143.32	6.351%	$152.4223	$152.42	$152.40	$152.40
Purchase #7	$97.31	12.279%	$109.2587	$109.26	$109.25	$109.30
7 purchase totals =	$861.37		$940.4185	$940.41	$940.40	$940.50