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	$86.96	4.389%	$90.7767	$90.78	$90.80	$90.80
Purchase #2	$124.87	10.343%	$137.7853	$137.79	$137.80	$137.80
Purchase #3	$43.77	8.713%	$47.5837	$47.58	$47.60	$47.60
Purchase #4	$124.49	13.671%	$141.509	$141.51	$141.50	$141.50
Purchase #5	$77.25	6.863%	$82.5517	$82.55	$82.55	$82.60
Purchase #6	$50.63	3.348%	$52.3251	$52.33	$52.35	$52.30
Purchase #7	$58.43	10.829%	$64.7574	$64.76	$64.75	$64.80
7 purchase totals =	$566.40		$617.2889	$617.30	$617.35	$617.40