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	$147.35	12.859%	$166.2977	$166.30	$166.30	$166.30
Purchase #2	$80.28	4.631%	$83.9978	$84.00	$84.00	$84.00
Purchase #3	$18.55	12.240%	$20.8205	$20.82	$20.80	$20.80
Purchase #4	$168.28	4.756%	$176.2834	$176.28	$176.30	$176.30
Purchase #5	$73.75	6.860%	$78.8093	$78.81	$78.80	$78.80
Purchase #6	$11.58	13.121%	$13.0994	$13.10	$13.10	$13.10
Purchase #7	$86.39	4.465%	$90.2473	$90.25	$90.25	$90.20
7 purchase totals =	$586.18		$629.5554	$629.56	$629.55	$629.50