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	$152.99	12.391%	$171.947	$171.95	$171.95	$171.90
Purchase #2	$129.35	12.208%	$145.141	$145.14	$145.15	$145.10
Purchase #3	$103.33	8.230%	$111.8341	$111.83	$111.85	$111.80
Purchase #4	$82.67	4.632%	$86.4993	$86.50	$86.50	$86.50
Purchase #5	$70.81	9.265%	$77.3705	$77.37	$77.35	$77.40
Purchase #6	$129.71	7.160%	$138.9972	$139.00	$139.00	$139.00
Purchase #7	$223.71	8.125%	$241.8864	$241.89	$241.90	$241.90
7 purchase totals =	$892.57		$973.6755	$973.68	$973.70	$973.60