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	$233.49	6.176%	$247.9103	$247.91	$247.90	$247.90
Purchase #2	$220.39	6.548%	$234.8211	$234.82	$234.80	$234.80
Purchase #3	$63.58	4.303%	$66.3158	$66.32	$66.30	$66.30
Purchase #4	$59.41	11.151%	$66.0348	$66.03	$66.05	$66.00
Purchase #5	$37.90	13.231%	$42.9145	$42.91	$42.90	$42.90
Purchase #6	$43.36	13.674%	$49.289	$49.29	$49.30	$49.30
Purchase #7	$73.91	10.583%	$81.7319	$81.73	$81.75	$81.70
7 purchase totals =	$732.04		$789.0174	$789.01	$789.00	$788.90