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	$230.35	3.585%	$238.608	$238.61	$238.60	$238.60
Purchase #2	$24.55	12.121%	$27.5257	$27.53	$27.55	$27.50
Purchase #3	$26.28	7.759%	$28.3191	$28.32	$28.30	$28.30
Purchase #4	$87.98	13.404%	$99.7728	$99.77	$99.75	$99.80
Purchase #5	$106.91	8.852%	$116.3737	$116.37	$116.35	$116.40
Purchase #6	$42.48	11.105%	$47.1974	$47.20	$47.20	$47.20
Purchase #7	$170.28	5.341%	$179.3747	$179.37	$179.35	$179.40
7 purchase totals =	$688.83		$737.1714	$737.17	$737.10	$737.20