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	$225.90	12.583%	$254.325	$254.33	$254.35	$254.30
Purchase #2	$228.60	5.133%	$240.334	$240.33	$240.35	$240.30
Purchase #3	$83.97	9.385%	$91.8506	$91.85	$91.85	$91.90
Purchase #4	$63.91	13.575%	$72.5858	$72.59	$72.60	$72.60
Purchase #5	$47.78	10.546%	$52.8189	$52.82	$52.80	$52.80
Purchase #6	$57.30	7.634%	$61.6743	$61.67	$61.65	$61.70
Purchase #7	$60.30	10.578%	$66.6785	$66.68	$66.70	$66.70
7 purchase totals =	$767.76		$840.2671	$840.27	$840.30	$840.30