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	$38.26	5.561%	$40.3876	$40.39	$40.40	$40.40
Purchase #2	$145.63	6.178%	$154.627	$154.63	$154.65	$154.60
Purchase #3	$123.83	12.230%	$138.9744	$138.97	$138.95	$139.00
Purchase #4	$61.86	5.274%	$65.1225	$65.12	$65.10	$65.10
Purchase #5	$25.25	12.689%	$28.454	$28.45	$28.45	$28.50
Purchase #6	$44.75	4.198%	$46.6286	$46.63	$46.65	$46.60
Purchase #7	$80.60	10.593%	$89.138	$89.14	$89.15	$89.10
7 purchase totals =	$520.18		$563.3321	$563.33	$563.35	$563.30