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	$223.71	5.197%	$235.3362	$235.34	$235.35	$235.30
Purchase #2	$61.91	13.541%	$70.2932	$70.29	$70.30	$70.30
Purchase #3	$9.45	6.781%	$10.0908	$10.09	$10.10	$10.10
Purchase #4	$46.58	3.171%	$48.0571	$48.06	$48.05	$48.10
Purchase #5	$240.91	7.436%	$258.8241	$258.82	$258.80	$258.80
Purchase #6	$66.33	8.692%	$72.0954	$72.10	$72.10	$72.10
Purchase #7	$134.63	4.651%	$140.8916	$140.89	$140.90	$140.90
7 purchase totals =	$783.52		$835.5884	$835.59	$835.60	$835.60