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	$150.26	3.467%	$155.4695	$155.47	$155.45	$155.50
Purchase #2	$105.40	12.512%	$118.5876	$118.59	$118.60	$118.60
Purchase #3	$205.89	5.237%	$216.6725	$216.67	$216.65	$216.70
Purchase #4	$210.56	13.552%	$239.0951	$239.10	$239.10	$239.10
Purchase #5	$95.92	13.867%	$109.2212	$109.22	$109.20	$109.20
Purchase #6	$12.53	10.246%	$13.8138	$13.81	$13.80	$13.80
Purchase #7	$137.58	9.420%	$150.54	$150.54	$150.55	$150.50
7 purchase totals =	$918.14		$1,003.3997	$1,003.40	$1,003.35	$1,003.40