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	$63.30	12.517%	$71.2233	$71.22	$71.20	$71.20
Purchase #2	$121.99	7.344%	$130.9489	$130.95	$130.95	$130.90
Purchase #3	$127.94	6.771%	$136.6028	$136.60	$136.60	$136.60
Purchase #4	$168.68	9.584%	$184.8463	$184.85	$184.85	$184.80
Purchase #5	$104.42	7.607%	$112.3632	$112.36	$112.35	$112.40
Purchase #6	$88.82	13.296%	$100.6295	$100.63	$100.65	$100.60
Purchase #7	$127.89	11.247%	$142.2738	$142.27	$142.25	$142.30
7 purchase totals =	$803.04		$878.8878	$878.88	$878.85	$878.80