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	$239.56	13.786%	$272.5857	$272.59	$272.60	$272.60
Purchase #2	$92.39	11.858%	$103.3456	$103.35	$103.35	$103.30
Purchase #3	$233.41	6.190%	$247.8581	$247.86	$247.85	$247.90
Purchase #4	$207.81	7.578%	$223.5578	$223.56	$223.55	$223.60
Purchase #5	$68.67	12.748%	$77.4241	$77.42	$77.40	$77.40
Purchase #6	$92.83	3.124%	$95.73	$95.73	$95.75	$95.70
Purchase #7	$28.40	5.333%	$29.9146	$29.91	$29.90	$29.90
7 purchase totals =	$963.07		$1,050.4159	$1,050.42	$1,050.40	$1,050.40