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	$50.65	6.279%	$53.8303	$53.83	$53.85	$53.80
Purchase #2	$180.66	10.368%	$199.3908	$199.39	$199.40	$199.40
Purchase #3	$37.48	6.678%	$39.9829	$39.98	$40.00	$40.00
Purchase #4	$38.53	5.257%	$40.5555	$40.56	$40.55	$40.60
Purchase #5	$74.40	9.700%	$81.6168	$81.62	$81.60	$81.60
Purchase #6	$219.88	13.595%	$249.7727	$249.77	$249.75	$249.80
Purchase #7	$145.35	6.674%	$155.0507	$155.05	$155.05	$155.10
7 purchase totals =	$746.95		$820.1997	$820.20	$820.20	$820.30