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	$231.80	3.530%	$239.9825	$239.98	$240.00	$240.00
Purchase #2	$87.95	9.716%	$96.4952	$96.50	$96.50	$96.50
Purchase #3	$114.28	8.797%	$124.3332	$124.33	$124.35	$124.30
Purchase #4	$74.95	4.407%	$78.253	$78.25	$78.25	$78.30
Purchase #5	$80.40	12.639%	$90.5618	$90.56	$90.55	$90.60
Purchase #6	$130.78	12.215%	$146.7548	$146.75	$146.75	$146.80
Purchase #7	$172.33	12.647%	$194.1246	$194.12	$194.10	$194.10
7 purchase totals =	$892.49		$970.5051	$970.49	$970.50	$970.60