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	$136.51	7.431%	$146.6541	$146.65	$146.65	$146.70
Purchase #2	$76.82	7.168%	$82.3265	$82.33	$82.35	$82.30
Purchase #3	$100.72	11.626%	$112.4297	$112.43	$112.45	$112.40
Purchase #4	$22.93	7.762%	$24.7098	$24.71	$24.70	$24.70
Purchase #5	$81.78	10.249%	$90.1616	$90.16	$90.15	$90.20
Purchase #6	$103.99	10.870%	$115.2937	$115.29	$115.30	$115.30
Purchase #7	$29.29	9.332%	$32.0233	$32.02	$32.00	$32.00
7 purchase totals =	$552.04		$603.5987	$603.59	$603.60	$603.60