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	$177.42	5.351%	$186.9137	$186.91	$186.90	$186.90
Purchase #2	$57.81	9.748%	$63.4453	$63.45	$63.45	$63.40
Purchase #3	$151.57	5.162%	$159.394	$159.39	$159.40	$159.40
Purchase #4	$50.59	10.364%	$55.8331	$55.83	$55.85	$55.80
Purchase #5	$35.49	12.870%	$40.0576	$40.06	$40.05	$40.10
Purchase #6	$81.82	11.298%	$91.064	$91.06	$91.05	$91.10
Purchase #7	$231.80	6.837%	$247.6482	$247.65	$247.65	$247.60
7 purchase totals =	$786.50		$844.3559	$844.35	$844.35	$844.30