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	$58.60	13.693%	$66.6241	$66.62	$66.60	$66.60
Purchase #2	$61.75	8.595%	$67.0574	$67.06	$67.05	$67.10
Purchase #3	$182.47	8.517%	$198.011	$198.01	$198.00	$198.00
Purchase #4	$188.43	5.672%	$199.1177	$199.12	$199.10	$199.10
Purchase #5	$29.63	7.691%	$31.9088	$31.91	$31.90	$31.90
Purchase #6	$31.90	13.233%	$36.1213	$36.12	$36.10	$36.10
Purchase #7	$176.85	13.463%	$200.6593	$200.66	$200.65	$200.70
7 purchase totals =	$729.63		$799.4996	$799.50	$799.40	$799.50