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	$25.86	12.590%	$29.1158	$29.12	$29.10	$29.10
Purchase #2	$113.45	8.618%	$123.2271	$123.23	$123.25	$123.20
Purchase #3	$43.30	11.504%	$48.2812	$48.28	$48.30	$48.30
Purchase #4	$56.88	8.862%	$61.9207	$61.92	$61.90	$61.90
Purchase #5	$39.58	7.176%	$42.4203	$42.42	$42.40	$42.40
Purchase #6	$21.64	11.758%	$24.1844	$24.18	$24.20	$24.20
Purchase #7	$195.87	11.233%	$217.8721	$217.87	$217.85	$217.90
7 purchase totals =	$496.58		$547.0216	$547.02	$547.00	$547.00