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	$70.27	5.118%	$73.8664	$73.87	$73.85	$73.90
Purchase #2	$209.92	12.285%	$235.7087	$235.71	$235.70	$235.70
Purchase #3	$11.71	6.422%	$12.462	$12.46	$12.45	$12.50
Purchase #4	$121.60	13.149%	$137.5892	$137.59	$137.60	$137.60
Purchase #5	$70.35	4.450%	$73.4806	$73.48	$73.50	$73.50
Purchase #6	$130.30	5.349%	$137.2697	$137.27	$137.25	$137.30
Purchase #7	$42.37	3.383%	$43.8034	$43.80	$43.80	$43.80
7 purchase totals =	$656.52		$714.1800	$714.18	$714.15	$714.30