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	$159.25	13.855%	$181.3141	$181.31	$181.30	$181.30
Purchase #2	$102.97	11.844%	$115.1658	$115.17	$115.15	$115.20
Purchase #3	$88.60	3.327%	$91.5477	$91.55	$91.55	$91.50
Purchase #4	$248.54	7.594%	$267.4141	$267.41	$267.40	$267.40
Purchase #5	$154.25	12.732%	$173.8891	$173.89	$173.90	$173.90
Purchase #6	$14.69	5.686%	$15.5253	$15.53	$15.55	$15.50
Purchase #7	$88.31	13.734%	$100.4385	$100.44	$100.45	$100.40
7 purchase totals =	$856.61		$945.2946	$945.30	$945.30	$945.20