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	$45.36	13.330%	$51.4065	$51.41	$51.40	$51.40
Purchase #2	$133.61	4.354%	$139.4274	$139.43	$139.45	$139.40
Purchase #3	$178.39	5.451%	$188.114	$188.11	$188.10	$188.10
Purchase #4	$40.44	4.690%	$42.3366	$42.34	$42.35	$42.30
Purchase #5	$52.79	3.449%	$54.6107	$54.61	$54.60	$54.60
Purchase #6	$111.84	5.317%	$117.7865	$117.79	$117.80	$117.80
Purchase #7	$20.97	9.397%	$22.9406	$22.94	$22.95	$22.90
7 purchase totals =	$583.40		$616.6223	$616.63	$616.65	$616.50