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	$122.91	11.695%	$137.2843	$137.28	$137.30	$137.30
Purchase #2	$65.90	12.679%	$74.2555	$74.26	$74.25	$74.30
Purchase #3	$235.45	13.761%	$267.8503	$267.85	$267.85	$267.90
Purchase #4	$222.78	4.633%	$233.1014	$233.10	$233.10	$233.10
Purchase #5	$68.35	4.666%	$71.5392	$71.54	$71.55	$71.50
Purchase #6	$70.89	13.372%	$80.3694	$80.37	$80.35	$80.40
Purchase #7	$152.38	4.224%	$158.8165	$158.82	$158.80	$158.80
7 purchase totals =	$938.66		$1,023.2166	$1,023.22	$1,023.20	$1,023.30