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	$103.50	5.371%	$109.059	$109.06	$109.05	$109.10
Purchase #2	$119.42	12.474%	$134.3165	$134.32	$134.30	$134.30
Purchase #3	$104.89	3.490%	$108.5507	$108.55	$108.55	$108.60
Purchase #4	$133.43	13.268%	$151.1335	$151.13	$151.15	$151.10
Purchase #5	$234.78	8.787%	$255.4101	$255.41	$255.40	$255.40
Purchase #6	$88.35	4.324%	$92.1703	$92.17	$92.15	$92.20
Purchase #7	$18.89	7.541%	$20.3145	$20.31	$20.30	$20.30
7 purchase totals =	$803.26		$870.9546	$870.95	$870.90	$871.00