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	$162.44	10.405%	$179.3419	$179.34	$179.35	$179.30
Purchase #2	$40.86	10.872%	$45.3023	$45.30	$45.30	$45.30
Purchase #3	$185.27	12.719%	$208.8345	$208.83	$208.85	$208.80
Purchase #4	$193.84	12.409%	$217.8936	$217.89	$217.90	$217.90
Purchase #5	$24.71	6.163%	$26.2329	$26.23	$26.25	$26.20
Purchase #6	$66.94	5.758%	$70.7944	$70.79	$70.80	$70.80
Purchase #7	$82.41	10.597%	$91.143	$91.14	$91.15	$91.10
7 purchase totals =	$756.47		$839.5426	$839.52	$839.60	$839.40