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	$95.77	4.108%	$99.7042	$99.70	$99.70	$99.70
Purchase #2	$113.96	5.530%	$120.262	$120.26	$120.25	$120.30
Purchase #3	$50.87	13.132%	$57.5502	$57.55	$57.55	$57.60
Purchase #4	$87.78	11.723%	$98.0704	$98.07	$98.05	$98.10
Purchase #5	$96.91	12.565%	$109.0867	$109.09	$109.10	$109.10
Purchase #6	$99.65	11.643%	$111.2522	$111.25	$111.25	$111.30
Purchase #7	$136.84	5.590%	$144.4894	$144.49	$144.50	$144.50
7 purchase totals =	$681.78		$740.4151	$740.41	$740.40	$740.60