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	$152.34	3.227%	$157.256	$157.26	$157.25	$157.30
Purchase #2	$104.59	6.336%	$111.2168	$111.22	$111.20	$111.20
Purchase #3	$89.95	10.850%	$99.7096	$99.71	$99.70	$99.70
Purchase #4	$224.98	12.408%	$252.8955	$252.90	$252.90	$252.90
Purchase #5	$156.90	6.316%	$166.8098	$166.81	$166.80	$166.80
Purchase #6	$35.76	8.719%	$38.8779	$38.88	$38.90	$38.90
Purchase #7	$242.96	12.376%	$273.0287	$273.03	$273.05	$273.00
7 purchase totals =	$1,007.48		$1,099.7943	$1,099.81	$1,099.80	$1,099.80