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	$44.82	12.239%	$50.3055	$50.31	$50.30	$50.30
Purchase #2	$96.33	7.360%	$103.4199	$103.42	$103.40	$103.40
Purchase #3	$137.27	7.129%	$147.056	$147.06	$147.05	$147.10
Purchase #4	$37.88	7.332%	$40.6574	$40.66	$40.65	$40.70
Purchase #5	$10.66	8.683%	$11.5856	$11.59	$11.60	$11.60
Purchase #6	$37.62	10.680%	$41.6378	$41.64	$41.65	$41.60
Purchase #7	$63.52	13.329%	$71.9866	$71.99	$72.00	$72.00
7 purchase totals =	$428.10		$466.6488	$466.67	$466.65	$466.70