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	$150.43	7.610%	$161.8777	$161.88	$161.90	$161.90
Purchase #2	$114.40	5.754%	$120.9826	$120.98	$121.00	$121.00
Purchase #3	$222.67	9.510%	$243.8459	$243.85	$243.85	$243.80
Purchase #4	$176.52	13.818%	$200.9115	$200.91	$200.90	$200.90
Purchase #5	$92.59	10.821%	$102.6092	$102.61	$102.60	$102.60
Purchase #6	$60.28	3.639%	$62.4736	$62.47	$62.45	$62.50
Purchase #7	$96.99	3.864%	$100.7377	$100.74	$100.75	$100.70
7 purchase totals =	$913.88		$993.4382	$993.44	$993.45	$993.40