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	$18.75	4.255%	$19.5478	$19.55	$19.55	$19.50
Purchase #2	$93.43	13.849%	$106.3691	$106.37	$106.35	$106.40
Purchase #3	$42.56	11.758%	$47.5642	$47.56	$47.55	$47.60
Purchase #4	$96.45	3.619%	$99.9405	$99.94	$99.95	$99.90
Purchase #5	$86.54	6.193%	$91.8994	$91.90	$91.90	$91.90
Purchase #6	$97.96	5.402%	$103.2518	$103.25	$103.25	$103.30
Purchase #7	$233.77	7.192%	$250.5827	$250.58	$250.60	$250.60
7 purchase totals =	$669.46		$719.1555	$719.15	$719.15	$719.20