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	$78.76	13.585%	$89.4595	$89.46	$89.45	$89.50
Purchase #2	$250.42	8.106%	$270.719	$270.72	$270.70	$270.70
Purchase #3	$238.73	6.840%	$255.0591	$255.06	$255.05	$255.10
Purchase #4	$11.32	13.498%	$12.848	$12.85	$12.85	$12.80
Purchase #5	$97.56	10.758%	$108.0555	$108.06	$108.05	$108.10
Purchase #6	$53.35	6.539%	$56.8386	$56.84	$56.85	$56.80
Purchase #7	$175.48	6.153%	$186.2773	$186.28	$186.30	$186.30
7 purchase totals =	$905.62		$979.2570	$979.27	$979.25	$979.30