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	$85.45	5.388%	$90.054	$90.05	$90.05	$90.10
Purchase #2	$117.99	8.156%	$127.6133	$127.61	$127.60	$127.60
Purchase #3	$185.49	8.675%	$201.5813	$201.58	$201.60	$201.60
Purchase #4	$43.54	13.410%	$49.3787	$49.38	$49.40	$49.40
Purchase #5	$190.69	6.497%	$203.0791	$203.08	$203.10	$203.10
Purchase #6	$200.40	8.788%	$218.0112	$218.01	$218.00	$218.00
Purchase #7	$104.33	3.660%	$108.1485	$108.15	$108.15	$108.10
7 purchase totals =	$927.89		$997.8661	$997.86	$997.90	$997.90