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	$112.42	13.168%	$127.2235	$127.22	$127.20	$127.20
Purchase #2	$123.66	5.175%	$130.0594	$130.06	$130.05	$130.10
Purchase #3	$27.81	13.694%	$31.6183	$31.62	$31.60	$31.60
Purchase #4	$115.88	9.688%	$127.1065	$127.11	$127.10	$127.10
Purchase #5	$63.61	8.238%	$68.8502	$68.85	$68.85	$68.90
Purchase #6	$218.78	7.263%	$234.67	$234.67	$234.65	$234.70
Purchase #7	$181.56	3.189%	$187.3499	$187.35	$187.35	$187.30
7 purchase totals =	$843.72		$906.8778	$906.88	$906.80	$906.90