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	$71.92	11.206%	$79.9794	$79.98	$80.00	$80.00
Purchase #2	$112.53	12.763%	$126.8922	$126.89	$126.90	$126.90
Purchase #3	$81.73	11.671%	$91.2687	$91.27	$91.25	$91.30
Purchase #4	$135.55	5.657%	$143.2181	$143.22	$143.20	$143.20
Purchase #5	$151.27	7.215%	$162.1841	$162.18	$162.20	$162.20
Purchase #6	$152.75	6.109%	$162.0815	$162.08	$162.10	$162.10
Purchase #7	$156.68	10.294%	$172.8086	$172.81	$172.80	$172.80
7 purchase totals =	$862.43		$938.4326	$938.43	$938.45	$938.50