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	$33.99	12.547%	$38.2547	$38.25	$38.25	$38.30
Purchase #2	$135.80	6.265%	$144.3079	$144.31	$144.30	$144.30
Purchase #3	$230.92	11.158%	$256.6861	$256.69	$256.70	$256.70
Purchase #4	$142.98	5.304%	$150.5637	$150.56	$150.55	$150.60
Purchase #5	$234.33	10.728%	$259.4689	$259.47	$259.45	$259.50
Purchase #6	$140.34	11.509%	$156.4917	$156.49	$156.50	$156.50
Purchase #7	$143.94	5.603%	$152.005	$152.01	$152.00	$152.00
7 purchase totals =	$1,062.30		$1,157.7780	$1,157.78	$1,157.75	$1,157.90