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	$59.80	10.645%	$66.1657	$66.17	$66.15	$66.20
Purchase #2	$101.50	4.584%	$106.1528	$106.15	$106.15	$106.20
Purchase #3	$141.32	10.637%	$156.3522	$156.35	$156.35	$156.40
Purchase #4	$62.36	7.660%	$67.1368	$67.14	$67.15	$67.10
Purchase #5	$32.37	5.161%	$34.0406	$34.04	$34.05	$34.00
Purchase #6	$65.27	11.265%	$72.6227	$72.62	$72.60	$72.60
Purchase #7	$98.60	11.786%	$110.221	$110.22	$110.20	$110.20
7 purchase totals =	$561.22		$612.6918	$612.69	$612.65	$612.70