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	$111.59	8.672%	$121.2671	$121.27	$121.25	$121.30
Purchase #2	$193.56	6.199%	$205.5588	$205.56	$205.55	$205.60
Purchase #3	$76.72	10.866%	$85.0564	$85.06	$85.05	$85.10
Purchase #4	$61.60	8.466%	$66.8151	$66.82	$66.80	$66.80
Purchase #5	$93.39	8.331%	$101.1703	$101.17	$101.15	$101.20
Purchase #6	$88.61	13.844%	$100.8772	$100.88	$100.90	$100.90
Purchase #7	$39.46	10.401%	$43.5642	$43.56	$43.55	$43.60
7 purchase totals =	$664.93		$724.3091	$724.32	$724.25	$724.50