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	$140.73	7.218%	$150.8879	$150.89	$150.90	$150.90
Purchase #2	$87.82	4.680%	$91.93	$91.93	$91.95	$91.90
Purchase #3	$176.90	3.738%	$183.5125	$183.51	$183.50	$183.50
Purchase #4	$133.48	13.241%	$151.1541	$151.15	$151.15	$151.20
Purchase #5	$162.27	13.718%	$184.5302	$184.53	$184.55	$184.50
Purchase #6	$203.52	12.741%	$229.4505	$229.45	$229.45	$229.50
Purchase #7	$65.90	13.167%	$74.5771	$74.58	$74.60	$74.60
7 purchase totals =	$970.62		$1,066.0423	$1,066.04	$1,066.10	$1,066.10