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	$89.98	6.365%	$95.7072	$95.71	$95.70	$95.70
Purchase #2	$15.95	7.827%	$17.1984	$17.20	$17.20	$17.20
Purchase #3	$99.90	9.765%	$109.6552	$109.66	$109.65	$109.70
Purchase #4	$195.95	3.336%	$202.4869	$202.49	$202.50	$202.50
Purchase #5	$37.25	4.303%	$38.8529	$38.85	$38.85	$38.90
Purchase #6	$76.90	10.544%	$85.0083	$85.01	$85.00	$85.00
Purchase #7	$38.56	10.478%	$42.6003	$42.60	$42.60	$42.60
7 purchase totals =	$554.49		$591.5092	$591.52	$591.50	$591.60