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	$235.30	12.361%	$264.3854	$264.39	$264.40	$264.40
Purchase #2	$223.34	9.633%	$244.8543	$244.85	$244.85	$244.90
Purchase #3	$249.52	9.833%	$274.0553	$274.06	$274.05	$274.10
Purchase #4	$46.57	3.288%	$48.1012	$48.10	$48.10	$48.10
Purchase #5	$133.41	4.495%	$139.4068	$139.41	$139.40	$139.40
Purchase #6	$11.61	8.622%	$12.611	$12.61	$12.60	$12.60
Purchase #7	$77.42	7.638%	$83.3333	$83.33	$83.35	$83.30
7 purchase totals =	$977.17		$1,066.7473	$1,066.75	$1,066.75	$1,066.80