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	$68.85	13.706%	$78.2866	$78.29	$78.30	$78.30
Purchase #2	$179.56	4.812%	$188.2004	$188.20	$188.20	$188.20
Purchase #3	$145.74	4.548%	$152.3683	$152.37	$152.35	$152.40
Purchase #4	$47.85	4.191%	$49.8554	$49.86	$49.85	$49.90
Purchase #5	$37.78	6.246%	$40.1397	$40.14	$40.15	$40.10
Purchase #6	$46.95	9.176%	$51.2581	$51.26	$51.25	$51.30
Purchase #7	$106.74	9.812%	$117.2133	$117.21	$117.20	$117.20
7 purchase totals =	$633.47		$677.3218	$677.33	$677.30	$677.40