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	$137.82	12.842%	$155.5188	$155.52	$155.50	$155.50
Purchase #2	$110.83	3.874%	$115.1236	$115.12	$115.10	$115.10
Purchase #3	$245.79	13.847%	$279.8245	$279.82	$279.80	$279.80
Purchase #4	$81.32	13.628%	$92.4023	$92.40	$92.40	$92.40
Purchase #5	$90.41	9.664%	$99.1472	$99.15	$99.15	$99.10
Purchase #6	$166.96	3.722%	$173.1743	$173.17	$173.15	$173.20
Purchase #7	$247.46	13.768%	$281.5303	$281.53	$281.55	$281.50
7 purchase totals =	$1,080.59		$1,196.7210	$1,196.71	$1,196.65	$1,196.60