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	$167.43	7.128%	$179.3644	$179.36	$179.35	$179.40
Purchase #2	$111.92	13.858%	$127.4299	$127.43	$127.45	$127.40
Purchase #3	$135.81	5.536%	$143.3284	$143.33	$143.35	$143.30
Purchase #4	$77.32	3.401%	$79.9497	$79.95	$79.95	$79.90
Purchase #5	$208.57	8.290%	$225.8605	$225.86	$225.85	$225.90
Purchase #6	$155.61	8.686%	$169.1263	$169.13	$169.15	$169.10
Purchase #7	$241.68	9.370%	$264.3254	$264.33	$264.35	$264.30
7 purchase totals =	$1,098.34		$1,189.3846	$1,189.39	$1,189.45	$1,189.30