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	$10.43	10.473%	$11.5223	$11.52	$11.50	$11.50
Purchase #2	$146.96	8.147%	$158.9328	$158.93	$158.95	$158.90
Purchase #3	$20.56	3.521%	$21.2839	$21.28	$21.30	$21.30
Purchase #4	$127.96	7.685%	$137.7937	$137.79	$137.80	$137.80
Purchase #5	$186.54	13.337%	$211.4188	$211.42	$211.40	$211.40
Purchase #6	$199.44	6.793%	$212.988	$212.99	$213.00	$213.00
Purchase #7	$39.27	9.151%	$42.8636	$42.86	$42.85	$42.90
7 purchase totals =	$731.16		$796.8031	$796.79	$796.80	$796.80