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	$227.58	10.839%	$252.2474	$252.25	$252.25	$252.20
Purchase #2	$139.74	13.169%	$158.1424	$158.14	$158.15	$158.10
Purchase #3	$241.67	3.221%	$249.4542	$249.45	$249.45	$249.50
Purchase #4	$13.62	13.523%	$15.4618	$15.46	$15.45	$15.50
Purchase #5	$123.81	3.241%	$127.8227	$127.82	$127.80	$127.80
Purchase #6	$187.77	4.835%	$196.8487	$196.85	$196.85	$196.80
Purchase #7	$88.32	5.352%	$93.0469	$93.05	$93.05	$93.00
7 purchase totals =	$1,022.51		$1,093.0241	$1,093.02	$1,093.00	$1,092.90