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	$211.54	5.144%	$222.4216	$222.42	$222.40	$222.40
Purchase #2	$202.44	12.424%	$227.5911	$227.59	$227.60	$227.60
Purchase #3	$52.75	4.699%	$55.2287	$55.23	$55.25	$55.20
Purchase #4	$125.39	7.294%	$134.5359	$134.54	$134.55	$134.50
Purchase #5	$48.60	11.470%	$54.1744	$54.17	$54.15	$54.20
Purchase #6	$132.98	8.567%	$144.3724	$144.37	$144.35	$144.40
Purchase #7	$91.34	6.381%	$97.1684	$97.17	$97.15	$97.20
7 purchase totals =	$865.04		$935.4925	$935.49	$935.45	$935.50