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	$170.55	8.176%	$184.4942	$184.49	$184.50	$184.50
Purchase #2	$89.78	10.118%	$98.8639	$98.86	$98.85	$98.90
Purchase #3	$116.57	9.263%	$127.3679	$127.37	$127.35	$127.40
Purchase #4	$167.99	3.795%	$174.3652	$174.37	$174.35	$174.40
Purchase #5	$163.94	7.716%	$176.5896	$176.59	$176.60	$176.60
Purchase #6	$50.55	8.621%	$54.9079	$54.91	$54.90	$54.90
Purchase #7	$67.26	7.285%	$72.1599	$72.16	$72.15	$72.20
7 purchase totals =	$826.64		$888.7486	$888.75	$888.70	$888.90