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	$151.50	7.665%	$163.1125	$163.11	$163.10	$163.10
Purchase #2	$29.84	10.250%	$32.8986	$32.90	$32.90	$32.90
Purchase #3	$231.52	9.797%	$254.202	$254.20	$254.20	$254.20
Purchase #4	$165.63	4.229%	$172.6345	$172.63	$172.65	$172.60
Purchase #5	$80.89	10.320%	$89.2378	$89.24	$89.25	$89.20
Purchase #6	$117.64	7.689%	$126.6853	$126.69	$126.70	$126.70
Purchase #7	$18.90	11.757%	$21.1221	$21.12	$21.10	$21.10
7 purchase totals =	$795.92		$859.8928	$859.89	$859.90	$859.80