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	$118.87	12.375%	$133.5802	$133.58	$133.60	$133.60
Purchase #2	$232.91	9.523%	$255.09	$255.09	$255.10	$255.10
Purchase #3	$234.96	6.246%	$249.6356	$249.64	$249.65	$249.60
Purchase #4	$67.64	4.295%	$70.5451	$70.55	$70.55	$70.50
Purchase #5	$49.47	7.746%	$53.3019	$53.30	$53.30	$53.30
Purchase #6	$28.25	12.183%	$31.6917	$31.69	$31.70	$31.70
Purchase #7	$183.79	13.561%	$208.7138	$208.71	$208.70	$208.70
7 purchase totals =	$915.89		$1,002.5583	$1,002.56	$1,002.60	$1,002.50