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	$160.75	8.166%	$173.8768	$173.88	$173.90	$173.90
Purchase #2	$68.87	12.345%	$77.372	$77.37	$77.35	$77.40
Purchase #3	$128.88	3.298%	$133.1305	$133.13	$133.15	$133.10
Purchase #4	$126.98	4.364%	$132.5214	$132.52	$132.50	$132.50
Purchase #5	$45.49	3.172%	$46.9329	$46.93	$46.95	$46.90
Purchase #6	$32.46	3.232%	$33.5091	$33.51	$33.50	$33.50
Purchase #7	$197.41	13.188%	$223.4444	$223.44	$223.45	$223.40
7 purchase totals =	$760.84		$820.7871	$820.78	$820.80	$820.70