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	$129.68	5.651%	$137.0082	$137.01	$137.00	$137.00
Purchase #2	$217.79	10.310%	$240.2441	$240.24	$240.25	$240.20
Purchase #3	$177.46	10.456%	$196.0152	$196.02	$196.00	$196.00
Purchase #4	$27.31	13.396%	$30.9684	$30.97	$30.95	$31.00
Purchase #5	$144.71	6.298%	$153.8238	$153.82	$153.80	$153.80
Purchase #6	$132.46	10.287%	$146.0862	$146.09	$146.10	$146.10
Purchase #7	$105.83	12.222%	$118.7645	$118.76	$118.75	$118.80
7 purchase totals =	$935.24		$1,022.9104	$1,022.91	$1,022.85	$1,022.90