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	$160.52	11.594%	$179.1307	$179.13	$179.15	$179.10
Purchase #2	$45.41	3.137%	$46.8345	$46.83	$46.85	$46.80
Purchase #3	$219.29	11.756%	$245.0697	$245.07	$245.05	$245.10
Purchase #4	$227.27	5.118%	$238.9017	$238.90	$238.90	$238.90
Purchase #5	$240.98	8.223%	$260.7958	$260.80	$260.80	$260.80
Purchase #6	$87.77	7.205%	$94.0938	$94.09	$94.10	$94.10
Purchase #7	$113.48	8.451%	$123.0702	$123.07	$123.05	$123.10
7 purchase totals =	$1,094.72		$1,187.8964	$1,187.89	$1,187.90	$1,187.90