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	$242.86	7.644%	$261.4242	$261.42	$261.40	$261.40
Purchase #2	$90.31	6.499%	$96.1792	$96.18	$96.20	$96.20
Purchase #3	$85.28	5.382%	$89.8698	$89.87	$89.85	$89.90
Purchase #4	$101.99	11.847%	$114.0728	$114.07	$114.05	$114.10
Purchase #5	$69.29	3.679%	$71.8392	$71.84	$71.85	$71.80
Purchase #6	$36.88	6.816%	$39.3937	$39.39	$39.40	$39.40
Purchase #7	$118.55	7.174%	$127.0548	$127.05	$127.05	$127.10
7 purchase totals =	$745.16		$799.8337	$799.82	$799.80	$799.90