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	$138.94	4.831%	$145.6522	$145.65	$145.65	$145.70
Purchase #2	$241.26	12.676%	$271.8421	$271.84	$271.85	$271.80
Purchase #3	$88.65	6.621%	$94.5195	$94.52	$94.50	$94.50
Purchase #4	$108.30	7.635%	$116.5687	$116.57	$116.55	$116.60
Purchase #5	$216.92	3.691%	$224.9265	$224.93	$224.95	$224.90
Purchase #6	$84.52	6.815%	$90.28	$90.28	$90.30	$90.30
Purchase #7	$105.69	10.530%	$116.8192	$116.82	$116.80	$116.80
7 purchase totals =	$984.28		$1,060.6082	$1,060.61	$1,060.60	$1,060.60