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	$53.43	12.141%	$59.9169	$59.92	$59.90	$59.90
Purchase #2	$73.95	12.339%	$83.0747	$83.07	$83.05	$83.10
Purchase #3	$183.59	9.267%	$200.6033	$200.60	$200.60	$200.60
Purchase #4	$38.31	9.840%	$42.0797	$42.08	$42.10	$42.10
Purchase #5	$28.42	5.404%	$29.9558	$29.96	$29.95	$30.00
Purchase #6	$208.91	12.255%	$234.5119	$234.51	$234.50	$234.50
Purchase #7	$93.54	3.805%	$97.0992	$97.10	$97.10	$97.10
7 purchase totals =	$680.15		$747.2415	$747.24	$747.20	$747.30