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	$9.94	8.519%	$10.7868	$10.79	$10.80	$10.80
Purchase #2	$249.26	3.544%	$258.0938	$258.09	$258.10	$258.10
Purchase #3	$245.46	13.592%	$278.8229	$278.82	$278.80	$278.80
Purchase #4	$81.55	11.443%	$90.8818	$90.88	$90.90	$90.90
Purchase #5	$200.49	10.536%	$221.6136	$221.61	$221.60	$221.60
Purchase #6	$204.69	8.585%	$222.2626	$222.26	$222.25	$222.30
Purchase #7	$104.61	5.670%	$110.5414	$110.54	$110.55	$110.50
7 purchase totals =	$1,096.00		$1,193.0029	$1,192.99	$1,193.00	$1,193.00