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	$34.30	12.500%	$38.5875	$38.59	$38.60	$38.60
Purchase #2	$186.78	13.796%	$212.5482	$212.55	$212.55	$212.50
Purchase #3	$135.38	12.113%	$151.7786	$151.78	$151.80	$151.80
Purchase #4	$114.72	10.746%	$127.0478	$127.05	$127.05	$127.00
Purchase #5	$91.68	8.375%	$99.3582	$99.36	$99.35	$99.40
Purchase #6	$129.33	13.340%	$146.5826	$146.58	$146.60	$146.60
Purchase #7	$206.85	13.236%	$234.2287	$234.23	$234.25	$234.20
7 purchase totals =	$899.04		$1,010.1316	$1,010.14	$1,010.20	$1,010.10