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	$46.69	10.211%	$51.4575	$51.46	$51.45	$51.50
Purchase #2	$99.88	11.720%	$111.5859	$111.59	$111.60	$111.60
Purchase #3	$64.35	13.539%	$73.0623	$73.06	$73.05	$73.10
Purchase #4	$137.63	6.379%	$146.4094	$146.41	$146.40	$146.40
Purchase #5	$41.47	5.273%	$43.6567	$43.66	$43.65	$43.70
Purchase #6	$31.98	10.287%	$35.2698	$35.27	$35.25	$35.30
Purchase #7	$167.79	13.422%	$190.3108	$190.31	$190.30	$190.30
7 purchase totals =	$589.79		$651.7524	$651.76	$651.70	$651.90