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	$183.37	9.180%	$200.2034	$200.20	$200.20	$200.20
Purchase #2	$34.53	4.560%	$36.1046	$36.10	$36.10	$36.10
Purchase #3	$173.88	8.154%	$188.0582	$188.06	$188.05	$188.10
Purchase #4	$46.51	10.451%	$51.3708	$51.37	$51.35	$51.40
Purchase #5	$101.55	9.865%	$111.5679	$111.57	$111.55	$111.60
Purchase #6	$35.58	13.298%	$40.3114	$40.31	$40.30	$40.30
Purchase #7	$156.98	6.279%	$166.8368	$166.84	$166.85	$166.80
7 purchase totals =	$732.40		$794.4531	$794.45	$794.40	$794.50