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	$92.41	7.201%	$99.0644	$99.06	$99.05	$99.10
Purchase #2	$213.89	3.716%	$221.8382	$221.84	$221.85	$221.80
Purchase #3	$34.77	10.274%	$38.3423	$38.34	$38.35	$38.30
Purchase #4	$106.72	9.529%	$116.8893	$116.89	$116.90	$116.90
Purchase #5	$41.41	12.733%	$46.6827	$46.68	$46.70	$46.70
Purchase #6	$28.60	13.663%	$32.5076	$32.51	$32.50	$32.50
Purchase #7	$218.64	7.293%	$234.5854	$234.59	$234.60	$234.60
7 purchase totals =	$736.44		$789.9099	$789.91	$789.95	$789.90