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	$143.86	5.306%	$151.4932	$151.49	$151.50	$151.50
Purchase #2	$120.81	13.745%	$137.4153	$137.42	$137.40	$137.40
Purchase #3	$70.98	10.319%	$78.3044	$78.30	$78.30	$78.30
Purchase #4	$71.84	7.315%	$77.0951	$77.10	$77.10	$77.10
Purchase #5	$13.34	9.739%	$14.6392	$14.64	$14.65	$14.60
Purchase #6	$129.35	11.775%	$144.581	$144.58	$144.60	$144.60
Purchase #7	$54.35	12.738%	$61.2731	$61.27	$61.25	$61.30
7 purchase totals =	$604.53		$664.8013	$664.80	$664.80	$664.80