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	$72.93	6.283%	$77.5122	$77.51	$77.50	$77.50
Purchase #2	$145.92	4.663%	$152.7242	$152.72	$152.70	$152.70
Purchase #3	$97.94	3.557%	$101.4237	$101.42	$101.40	$101.40
Purchase #4	$169.82	13.771%	$193.2059	$193.21	$193.20	$193.20
Purchase #5	$168.84	12.480%	$189.9112	$189.91	$189.90	$189.90
Purchase #6	$114.27	11.189%	$127.0557	$127.06	$127.05	$127.10
Purchase #7	$249.31	11.300%	$277.482	$277.48	$277.50	$277.50
7 purchase totals =	$1,019.03		$1,119.3149	$1,119.31	$1,119.25	$1,119.30