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	$127.90	12.715%	$144.1625	$144.16	$144.15	$144.20
Purchase #2	$59.39	11.537%	$66.2418	$66.24	$66.25	$66.20
Purchase #3	$219.29	13.467%	$248.8218	$248.82	$248.80	$248.80
Purchase #4	$153.39	8.260%	$166.06	$166.06	$166.05	$166.10
Purchase #5	$30.51	9.697%	$33.4686	$33.47	$33.45	$33.50
Purchase #6	$54.79	4.640%	$57.3323	$57.33	$57.35	$57.30
Purchase #7	$94.69	4.780%	$99.2162	$99.22	$99.20	$99.20
7 purchase totals =	$739.96		$815.3032	$815.30	$815.25	$815.30