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	$107.48	6.640%	$114.6167	$114.62	$114.60	$114.60
Purchase #2	$144.65	8.159%	$156.452	$156.45	$156.45	$156.50
Purchase #3	$226.48	10.560%	$250.3963	$250.40	$250.40	$250.40
Purchase #4	$78.32	5.389%	$82.5407	$82.54	$82.55	$82.50
Purchase #5	$239.74	6.568%	$255.4861	$255.49	$255.50	$255.50
Purchase #6	$121.55	11.338%	$135.3313	$135.33	$135.35	$135.30
Purchase #7	$225.91	13.298%	$255.9515	$255.95	$255.95	$256.00
7 purchase totals =	$1,144.13		$1,250.7746	$1,250.78	$1,250.80	$1,250.80