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	$38.57	10.330%	$42.5543	$42.55	$42.55	$42.60
Purchase #2	$40.36	3.443%	$41.7496	$41.75	$41.75	$41.70
Purchase #3	$95.91	12.842%	$108.2268	$108.23	$108.25	$108.20
Purchase #4	$185.60	10.522%	$205.1288	$205.13	$205.15	$205.10
Purchase #5	$80.75	7.260%	$86.6125	$86.61	$86.60	$86.60
Purchase #6	$142.26	4.575%	$148.7684	$148.77	$148.75	$148.80
Purchase #7	$222.61	6.697%	$237.5182	$237.52	$237.50	$237.50
7 purchase totals =	$806.06		$870.5586	$870.56	$870.55	$870.50