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	$134.66	7.583%	$144.8713	$144.87	$144.85	$144.90
Purchase #2	$215.54	5.426%	$227.2352	$227.24	$227.25	$227.20
Purchase #3	$44.26	12.559%	$49.8186	$49.82	$49.80	$49.80
Purchase #4	$78.79	5.550%	$83.1628	$83.16	$83.15	$83.20
Purchase #5	$249.59	7.748%	$268.9282	$268.93	$268.95	$268.90
Purchase #6	$24.72	12.176%	$27.7299	$27.73	$27.75	$27.70
Purchase #7	$51.98	5.639%	$54.9112	$54.91	$54.90	$54.90
7 purchase totals =	$799.54		$856.6572	$856.66	$856.65	$856.60