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	$81.48	9.841%	$89.4984	$89.50	$89.50	$89.50
Purchase #2	$217.82	6.329%	$231.6058	$231.61	$231.60	$231.60
Purchase #3	$173.80	7.551%	$186.9236	$186.92	$186.90	$186.90
Purchase #4	$10.43	10.860%	$11.5627	$11.56	$11.55	$11.60
Purchase #5	$161.79	10.567%	$178.8863	$178.89	$178.90	$178.90
Purchase #6	$179.75	11.416%	$200.2703	$200.27	$200.25	$200.30
Purchase #7	$36.86	13.415%	$41.8048	$41.80	$41.80	$41.80
7 purchase totals =	$861.93		$940.5519	$940.55	$940.50	$940.60