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	$200.27	13.786%	$227.8792	$227.88	$227.90	$227.90
Purchase #2	$38.38	11.398%	$42.7546	$42.75	$42.75	$42.80
Purchase #3	$46.95	9.135%	$51.2389	$51.24	$51.25	$51.20
Purchase #4	$59.70	13.240%	$67.6043	$67.60	$67.60	$67.60
Purchase #5	$174.29	12.335%	$195.7887	$195.79	$195.80	$195.80
Purchase #6	$56.55	11.109%	$62.8321	$62.83	$62.85	$62.80
Purchase #7	$138.79	4.322%	$144.7885	$144.79	$144.80	$144.80
7 purchase totals =	$714.93		$792.8863	$792.88	$792.95	$792.90