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	$94.38	6.855%	$100.8497	$100.85	$100.85	$100.80
Purchase #2	$153.48	9.158%	$167.5357	$167.54	$167.55	$167.50
Purchase #3	$239.63	6.772%	$255.8577	$255.86	$255.85	$255.90
Purchase #4	$107.52	12.537%	$120.9998	$121.00	$121.00	$121.00
Purchase #5	$198.50	6.488%	$211.3787	$211.38	$211.40	$211.40
Purchase #6	$59.84	3.152%	$61.7262	$61.73	$61.75	$61.70
Purchase #7	$36.31	7.860%	$39.164	$39.16	$39.15	$39.20
7 purchase totals =	$889.66		$957.5118	$957.52	$957.55	$957.50