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	$244.92	6.372%	$260.5263	$260.53	$260.55	$260.50
Purchase #2	$79.32	3.549%	$82.1351	$82.14	$82.15	$82.10
Purchase #3	$194.77	12.369%	$218.8611	$218.86	$218.85	$218.90
Purchase #4	$108.82	7.458%	$116.9358	$116.94	$116.95	$116.90
Purchase #5	$146.49	10.495%	$161.8641	$161.86	$161.85	$161.90
Purchase #6	$43.89	11.563%	$48.965	$48.97	$48.95	$49.00
Purchase #7	$140.66	6.828%	$150.2643	$150.26	$150.25	$150.30
7 purchase totals =	$958.87		$1,039.5517	$1,039.56	$1,039.55	$1,039.60