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	$30.91	7.757%	$33.3077	$33.31	$33.30	$33.30
Purchase #2	$217.42	13.865%	$247.5653	$247.57	$247.55	$247.60
Purchase #3	$142.45	5.792%	$150.7007	$150.70	$150.70	$150.70
Purchase #4	$102.66	9.507%	$112.4199	$112.42	$112.40	$112.40
Purchase #5	$62.50	8.245%	$67.6531	$67.65	$67.65	$67.70
Purchase #6	$144.64	12.622%	$162.8965	$162.90	$162.90	$162.90
Purchase #7	$119.48	3.433%	$123.5817	$123.58	$123.60	$123.60
7 purchase totals =	$820.06		$898.1249	$898.13	$898.10	$898.20