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	$231.90	12.708%	$261.3699	$261.37	$261.35	$261.40
Purchase #2	$240.65	4.411%	$251.2651	$251.27	$251.25	$251.30
Purchase #3	$6.96	5.584%	$7.3486	$7.35	$7.35	$7.30
Purchase #4	$132.54	8.874%	$144.3016	$144.30	$144.30	$144.30
Purchase #5	$80.78	12.213%	$90.6457	$90.65	$90.65	$90.60
Purchase #6	$93.67	12.605%	$105.4771	$105.48	$105.50	$105.50
Purchase #7	$27.96	5.162%	$29.4033	$29.40	$29.40	$29.40
7 purchase totals =	$814.46		$889.8113	$889.82	$889.80	$889.80