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	$123.38	13.629%	$140.1955	$140.20	$140.20	$140.20
Purchase #2	$32.65	5.701%	$34.5114	$34.51	$34.50	$34.50
Purchase #3	$158.67	7.720%	$170.9193	$170.92	$170.90	$170.90
Purchase #4	$84.58	5.784%	$89.4721	$89.47	$89.45	$89.50
Purchase #5	$144.83	5.723%	$153.1186	$153.12	$153.10	$153.10
Purchase #6	$135.92	12.506%	$152.9182	$152.92	$152.90	$152.90
Purchase #7	$165.49	13.347%	$187.578	$187.58	$187.60	$187.60
7 purchase totals =	$845.52		$928.7131	$928.72	$928.65	$928.70