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	$46.75	9.244%	$51.0716	$51.07	$51.05	$51.10
Purchase #2	$205.94	11.427%	$229.4728	$229.47	$229.45	$229.50
Purchase #3	$163.60	13.175%	$185.1543	$185.15	$185.15	$185.20
Purchase #4	$52.76	12.199%	$59.1962	$59.20	$59.20	$59.20
Purchase #5	$37.81	3.740%	$39.2241	$39.22	$39.20	$39.20
Purchase #6	$128.26	5.204%	$134.9347	$134.93	$134.95	$134.90
Purchase #7	$108.94	13.266%	$123.392	$123.39	$123.40	$123.40
7 purchase totals =	$744.06		$822.4457	$822.43	$822.40	$822.50