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	$116.77	9.547%	$127.918	$127.92	$127.90	$127.90
Purchase #2	$95.37	5.738%	$100.8423	$100.84	$100.85	$100.80
Purchase #3	$217.79	7.818%	$234.8168	$234.82	$234.80	$234.80
Purchase #4	$127.55	3.133%	$131.5461	$131.55	$131.55	$131.50
Purchase #5	$16.79	4.381%	$17.5256	$17.53	$17.55	$17.50
Purchase #6	$25.41	9.684%	$27.8707	$27.87	$27.85	$27.90
Purchase #7	$166.61	8.532%	$180.8252	$180.83	$180.85	$180.80
7 purchase totals =	$766.29		$821.3447	$821.36	$821.35	$821.20