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	$58.89	13.454%	$66.8131	$66.81	$66.80	$66.80
Purchase #2	$244.86	11.341%	$272.6296	$272.63	$272.65	$272.60
Purchase #3	$77.66	3.773%	$80.5901	$80.59	$80.60	$80.60
Purchase #4	$186.67	3.645%	$193.4741	$193.47	$193.45	$193.50
Purchase #5	$33.77	11.174%	$37.5435	$37.54	$37.55	$37.50
Purchase #6	$134.42	8.668%	$146.0715	$146.07	$146.05	$146.10
Purchase #7	$186.41	10.448%	$205.8861	$205.89	$205.90	$205.90
7 purchase totals =	$922.68		$1,003.0080	$1,003.00	$1,003.00	$1,003.00