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	$10.44	13.676%	$11.8678	$11.87	$11.85	$11.90
Purchase #2	$218.92	6.218%	$232.5324	$232.53	$232.55	$232.50
Purchase #3	$114.42	7.602%	$123.1182	$123.12	$123.10	$123.10
Purchase #4	$97.93	7.172%	$104.9535	$104.95	$104.95	$105.00
Purchase #5	$53.96	9.816%	$59.2567	$59.26	$59.25	$59.30
Purchase #6	$16.60	11.834%	$18.5644	$18.56	$18.55	$18.60
Purchase #7	$226.50	5.111%	$238.0764	$238.08	$238.10	$238.10
7 purchase totals =	$738.77		$788.3694	$788.37	$788.35	$788.50