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	$141.93	3.640%	$147.0963	$147.10	$147.10	$147.10
Purchase #2	$121.32	10.569%	$134.1423	$134.14	$134.15	$134.10
Purchase #3	$81.73	11.174%	$90.8625	$90.86	$90.85	$90.90
Purchase #4	$26.60	12.223%	$29.8513	$29.85	$29.85	$29.90
Purchase #5	$74.62	5.774%	$78.9286	$78.93	$78.95	$78.90
Purchase #6	$237.98	10.410%	$262.7537	$262.75	$262.75	$262.80
Purchase #7	$65.52	10.634%	$72.4874	$72.49	$72.50	$72.50
7 purchase totals =	$749.70		$816.1221	$816.12	$816.15	$816.20