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	$29.30	5.353%	$30.8684	$30.87	$30.85	$30.90
Purchase #2	$81.78	4.584%	$85.5288	$85.53	$85.55	$85.50
Purchase #3	$105.87	6.758%	$113.0247	$113.02	$113.00	$113.00
Purchase #4	$26.77	5.275%	$28.1821	$28.18	$28.20	$28.20
Purchase #5	$165.53	4.103%	$172.3217	$172.32	$172.30	$172.30
Purchase #6	$195.94	13.627%	$222.6407	$222.64	$222.65	$222.60
Purchase #7	$61.36	6.644%	$65.4368	$65.44	$65.45	$65.40
7 purchase totals =	$666.55		$718.0032	$718.00	$718.00	$717.90