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	$34.84	7.613%	$37.4924	$37.49	$37.50	$37.50
Purchase #2	$89.78	13.388%	$101.7997	$101.80	$101.80	$101.80
Purchase #3	$170.73	6.413%	$181.6789	$181.68	$181.70	$181.70
Purchase #4	$70.38	9.867%	$77.3244	$77.32	$77.30	$77.30
Purchase #5	$85.77	5.813%	$90.7558	$90.76	$90.75	$90.80
Purchase #6	$124.93	7.261%	$134.0012	$134.00	$134.00	$134.00
Purchase #7	$78.32	9.241%	$85.5576	$85.56	$85.55	$85.60
7 purchase totals =	$654.75		$708.6100	$708.61	$708.60	$708.70