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	$60.36	6.171%	$64.0848	$64.08	$64.10	$64.10
Purchase #2	$77.34	7.855%	$83.4151	$83.42	$83.40	$83.40
Purchase #3	$226.51	6.666%	$241.6092	$241.61	$241.60	$241.60
Purchase #4	$93.92	6.431%	$99.96	$99.96	$99.95	$100.00
Purchase #5	$100.49	10.771%	$111.3138	$111.31	$111.30	$111.30
Purchase #6	$127.53	7.475%	$137.0629	$137.06	$137.05	$137.10
Purchase #7	$201.56	4.154%	$209.9328	$209.93	$209.95	$209.90
7 purchase totals =	$887.71		$947.3786	$947.37	$947.35	$947.40