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	$228.99	9.639%	$251.0623	$251.06	$251.05	$251.10
Purchase #2	$138.73	6.159%	$147.2744	$147.27	$147.25	$147.30
Purchase #3	$118.82	7.164%	$127.3323	$127.33	$127.35	$127.30
Purchase #4	$70.82	7.627%	$76.2214	$76.22	$76.20	$76.20
Purchase #5	$14.92	3.861%	$15.4961	$15.50	$15.50	$15.50
Purchase #6	$171.77	9.658%	$188.3595	$188.36	$188.35	$188.40
Purchase #7	$166.43	11.385%	$185.3781	$185.38	$185.40	$185.40
7 purchase totals =	$910.48		$991.1241	$991.12	$991.10	$991.20