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	$74.39	5.851%	$78.7426	$78.74	$78.75	$78.70
Purchase #2	$188.57	9.388%	$206.273	$206.27	$206.25	$206.30
Purchase #3	$90.58	8.320%	$98.1163	$98.12	$98.10	$98.10
Purchase #4	$141.57	6.866%	$151.2902	$151.29	$151.30	$151.30
Purchase #5	$164.27	5.600%	$173.4691	$173.47	$173.45	$173.50
Purchase #6	$86.46	4.544%	$90.3887	$90.39	$90.40	$90.40
Purchase #7	$163.98	3.580%	$169.8505	$169.85	$169.85	$169.90
7 purchase totals =	$909.82		$968.1304	$968.13	$968.10	$968.20