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	$172.52	4.611%	$180.4749	$180.47	$180.45	$180.50
Purchase #2	$116.89	6.127%	$124.0519	$124.05	$124.05	$124.10
Purchase #3	$77.51	3.593%	$80.2949	$80.29	$80.30	$80.30
Purchase #4	$18.96	10.764%	$21.0009	$21.00	$21.00	$21.00
Purchase #5	$142.81	10.213%	$157.3952	$157.40	$157.40	$157.40
Purchase #6	$200.72	12.219%	$225.246	$225.25	$225.25	$225.20
Purchase #7	$45.41	10.605%	$50.2257	$50.23	$50.25	$50.20
7 purchase totals =	$774.82		$838.6895	$838.69	$838.70	$838.70