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	$119.30	9.707%	$130.8805	$130.88	$130.90	$130.90
Purchase #2	$206.79	7.758%	$222.8328	$222.83	$222.85	$222.80
Purchase #3	$131.93	13.239%	$149.3962	$149.40	$149.40	$149.40
Purchase #4	$34.62	8.732%	$37.643	$37.64	$37.65	$37.60
Purchase #5	$38.68	6.316%	$41.123	$41.12	$41.10	$41.10
Purchase #6	$37.37	9.595%	$40.9557	$40.96	$40.95	$41.00
Purchase #7	$85.88	4.790%	$89.9937	$89.99	$90.00	$90.00
7 purchase totals =	$654.57		$712.8249	$712.82	$712.85	$712.80