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	$108.34	6.455%	$115.3333	$115.33	$115.35	$115.30
Purchase #2	$50.95	6.598%	$54.3117	$54.31	$54.30	$54.30
Purchase #3	$163.47	6.453%	$174.0187	$174.02	$174.00	$174.00
Purchase #4	$10.90	3.866%	$11.3214	$11.32	$11.30	$11.30
Purchase #5	$92.78	9.160%	$101.2786	$101.28	$101.30	$101.30
Purchase #6	$33.82	10.382%	$37.3312	$37.33	$37.35	$37.30
Purchase #7	$18.38	4.869%	$19.2749	$19.27	$19.25	$19.30
7 purchase totals =	$478.64		$512.8698	$512.86	$512.85	$512.80