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	$97.34	6.263%	$103.4364	$103.44	$103.45	$103.40
Purchase #2	$144.87	4.247%	$151.0226	$151.02	$151.00	$151.00
Purchase #3	$160.39	5.669%	$169.4825	$169.48	$169.50	$169.50
Purchase #4	$80.78	9.779%	$88.6795	$88.68	$88.70	$88.70
Purchase #5	$131.41	7.662%	$141.4786	$141.48	$141.50	$141.50
Purchase #6	$43.75	9.458%	$47.8879	$47.89	$47.90	$47.90
Purchase #7	$128.32	4.641%	$134.2753	$134.28	$134.30	$134.30
7 purchase totals =	$786.86		$836.2628	$836.27	$836.35	$836.30