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	$217.89	6.380%	$231.7914	$231.79	$231.80	$231.80
Purchase #2	$158.46	13.817%	$180.3544	$180.35	$180.35	$180.40
Purchase #3	$168.32	12.287%	$189.0015	$189.00	$189.00	$189.00
Purchase #4	$105.81	5.614%	$111.7502	$111.75	$111.75	$111.80
Purchase #5	$142.78	12.306%	$160.3505	$160.35	$160.35	$160.40
Purchase #6	$239.30	9.517%	$262.0742	$262.07	$262.05	$262.10
Purchase #7	$175.45	13.336%	$198.848	$198.85	$198.85	$198.80
7 purchase totals =	$1,208.01		$1,334.1702	$1,334.16	$1,334.15	$1,334.30