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	$159.36	5.453%	$168.0499	$168.05	$168.05	$168.00
Purchase #2	$101.86	4.821%	$106.7707	$106.77	$106.75	$106.80
Purchase #3	$58.58	4.792%	$61.3872	$61.39	$61.40	$61.40
Purchase #4	$79.76	3.151%	$82.2732	$82.27	$82.25	$82.30
Purchase #5	$138.70	10.766%	$153.6324	$153.63	$153.65	$153.60
Purchase #6	$6.97	7.227%	$7.4737	$7.47	$7.45	$7.50
Purchase #7	$27.72	6.489%	$29.5188	$29.52	$29.50	$29.50
7 purchase totals =	$572.95		$609.1059	$609.10	$609.05	$609.10