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	$12.37	10.293%	$13.6432	$13.64	$13.65	$13.60
Purchase #2	$117.86	6.808%	$125.8839	$125.88	$125.90	$125.90
Purchase #3	$220.87	5.621%	$233.2851	$233.29	$233.30	$233.30
Purchase #4	$81.43	11.220%	$90.5664	$90.57	$90.55	$90.60
Purchase #5	$202.99	7.694%	$218.6081	$218.61	$218.60	$218.60
Purchase #6	$106.44	9.255%	$116.291	$116.29	$116.30	$116.30
Purchase #7	$122.88	3.790%	$127.5372	$127.54	$127.55	$127.50
7 purchase totals =	$864.84		$925.8149	$925.82	$925.85	$925.80