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	$216.47	11.249%	$240.8207	$240.82	$240.80	$240.80
Purchase #2	$186.46	13.408%	$211.4606	$211.46	$211.45	$211.50
Purchase #3	$44.90	4.345%	$46.8509	$46.85	$46.85	$46.90
Purchase #4	$149.77	13.521%	$170.0204	$170.02	$170.00	$170.00
Purchase #5	$90.49	10.417%	$99.9163	$99.92	$99.90	$99.90
Purchase #6	$83.50	9.603%	$91.5185	$91.52	$91.50	$91.50
Purchase #7	$38.87	6.376%	$41.3484	$41.35	$41.35	$41.30
7 purchase totals =	$810.46		$901.9358	$901.94	$901.85	$901.90