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	$30.78	8.803%	$33.4896	$33.49	$33.50	$33.50
Purchase #2	$217.27	11.203%	$241.6108	$241.61	$241.60	$241.60
Purchase #3	$38.41	8.791%	$41.7866	$41.79	$41.80	$41.80
Purchase #4	$48.57	10.294%	$53.5698	$53.57	$53.55	$53.60
Purchase #5	$90.78	5.824%	$96.067	$96.07	$96.05	$96.10
Purchase #6	$248.33	7.716%	$267.4911	$267.49	$267.50	$267.50
Purchase #7	$159.53	13.752%	$181.4686	$181.47	$181.45	$181.50
7 purchase totals =	$833.67		$915.4835	$915.49	$915.45	$915.60