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	$223.71	3.502%	$231.5443	$231.54	$231.55	$231.50
Purchase #2	$59.27	12.610%	$66.7439	$66.74	$66.75	$66.70
Purchase #3	$36.45	12.843%	$41.1313	$41.13	$41.15	$41.10
Purchase #4	$113.32	11.409%	$126.2487	$126.25	$126.25	$126.20
Purchase #5	$171.74	10.229%	$189.3073	$189.31	$189.30	$189.30
Purchase #6	$140.87	12.458%	$158.4196	$158.42	$158.40	$158.40
Purchase #7	$93.89	8.778%	$102.1317	$102.13	$102.15	$102.10
7 purchase totals =	$839.25		$915.5268	$915.52	$915.55	$915.30