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	$9.83	7.109%	$10.5288	$10.53	$10.55	$10.50
Purchase #2	$109.72	12.852%	$123.8212	$123.82	$123.80	$123.80
Purchase #3	$65.60	12.328%	$73.6872	$73.69	$73.70	$73.70
Purchase #4	$17.55	5.502%	$18.5156	$18.52	$18.50	$18.50
Purchase #5	$138.81	4.742%	$145.3924	$145.39	$145.40	$145.40
Purchase #6	$36.93	4.787%	$38.6978	$38.70	$38.70	$38.70
Purchase #7	$41.66	10.448%	$46.0126	$46.01	$46.00	$46.00
7 purchase totals =	$420.10		$456.6556	$456.66	$456.65	$456.60