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	$112.88	9.240%	$123.3101	$123.31	$123.30	$123.30
Purchase #2	$108.65	5.301%	$114.4095	$114.41	$114.40	$114.40
Purchase #3	$116.43	12.687%	$131.2015	$131.20	$131.20	$131.20
Purchase #4	$116.34	11.401%	$129.6039	$129.60	$129.60	$129.60
Purchase #5	$53.35	13.607%	$60.6093	$60.61	$60.60	$60.60
Purchase #6	$192.53	5.209%	$202.5589	$202.56	$202.55	$202.60
Purchase #7	$90.51	10.680%	$100.1765	$100.18	$100.20	$100.20
7 purchase totals =	$790.69		$861.8697	$861.87	$861.85	$861.90