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	$128.80	4.305%	$134.3448	$134.34	$134.35	$134.30
Purchase #2	$147.81	13.776%	$168.1723	$168.17	$168.15	$168.20
Purchase #3	$249.92	11.769%	$279.3331	$279.33	$279.35	$279.30
Purchase #4	$126.60	13.184%	$143.2909	$143.29	$143.30	$143.30
Purchase #5	$54.46	4.265%	$56.7827	$56.78	$56.80	$56.80
Purchase #6	$171.68	12.476%	$193.0988	$193.10	$193.10	$193.10
Purchase #7	$96.73	7.436%	$103.9228	$103.92	$103.90	$103.90
7 purchase totals =	$976.00		$1,078.9454	$1,078.93	$1,078.95	$1,078.90