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	$76.49	3.463%	$79.1388	$79.14	$79.15	$79.10
Purchase #2	$95.61	5.561%	$100.9269	$100.93	$100.95	$100.90
Purchase #3	$125.32	12.625%	$141.1417	$141.14	$141.15	$141.10
Purchase #4	$241.52	4.559%	$252.5309	$252.53	$252.55	$252.50
Purchase #5	$126.32	10.443%	$139.5116	$139.51	$139.50	$139.50
Purchase #6	$30.50	7.682%	$32.843	$32.84	$32.85	$32.80
Purchase #7	$83.89	12.265%	$94.1791	$94.18	$94.20	$94.20
7 purchase totals =	$779.65		$840.2720	$840.27	$840.35	$840.10