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	$12.95	6.478%	$13.7889	$13.79	$13.80	$13.80
Purchase #2	$222.28	5.782%	$235.1322	$235.13	$235.15	$235.10
Purchase #3	$103.31	10.774%	$114.4406	$114.44	$114.45	$114.40
Purchase #4	$236.62	10.842%	$262.2743	$262.27	$262.25	$262.30
Purchase #5	$106.45	11.692%	$118.8961	$118.90	$118.90	$118.90
Purchase #6	$69.61	12.393%	$78.2368	$78.24	$78.25	$78.20
Purchase #7	$38.68	3.711%	$40.1154	$40.12	$40.10	$40.10
7 purchase totals =	$789.90		$862.8843	$862.89	$862.90	$862.80