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	$246.70	9.665%	$270.5436	$270.54	$270.55	$270.50
Purchase #2	$54.66	4.582%	$57.1645	$57.16	$57.15	$57.20
Purchase #3	$212.74	4.112%	$221.4879	$221.49	$221.50	$221.50
Purchase #4	$239.27	4.744%	$250.621	$250.62	$250.60	$250.60
Purchase #5	$49.83	8.554%	$54.0925	$54.09	$54.10	$54.10
Purchase #6	$15.95	13.751%	$18.1433	$18.14	$18.15	$18.10
Purchase #7	$247.26	10.187%	$272.4484	$272.45	$272.45	$272.40
7 purchase totals =	$1,066.41		$1,144.5012	$1,144.49	$1,144.50	$1,144.40