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	$108.77	13.598%	$123.5605	$123.56	$123.55	$123.60
Purchase #2	$10.55	3.769%	$10.9476	$10.95	$10.95	$10.90
Purchase #3	$116.99	9.166%	$127.7133	$127.71	$127.70	$127.70
Purchase #4	$14.35	11.776%	$16.0399	$16.04	$16.05	$16.00
Purchase #5	$225.74	10.716%	$249.9303	$249.93	$249.95	$249.90
Purchase #6	$72.84	8.134%	$78.7648	$78.76	$78.75	$78.80
Purchase #7	$83.35	3.274%	$86.0789	$86.08	$86.10	$86.10
7 purchase totals =	$632.59		$693.0353	$693.03	$693.05	$693.00