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	$223.77	8.816%	$243.4976	$243.50	$243.50	$243.50
Purchase #2	$232.86	9.348%	$254.6278	$254.63	$254.65	$254.60
Purchase #3	$226.63	10.692%	$250.8613	$250.86	$250.85	$250.90
Purchase #4	$130.35	7.182%	$139.7117	$139.71	$139.70	$139.70
Purchase #5	$32.74	13.419%	$37.1334	$37.13	$37.15	$37.10
Purchase #6	$29.97	9.548%	$32.8315	$32.83	$32.85	$32.80
Purchase #7	$31.97	9.463%	$34.9953	$35.00	$35.00	$35.00
7 purchase totals =	$908.29		$993.6586	$993.66	$993.70	$993.60