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	$81.54	10.228%	$89.8799	$89.88	$89.90	$89.90
Purchase #2	$231.74	7.830%	$249.8852	$249.89	$249.90	$249.90
Purchase #3	$228.43	12.795%	$257.6576	$257.66	$257.65	$257.70
Purchase #4	$163.74	10.450%	$180.8508	$180.85	$180.85	$180.90
Purchase #5	$153.97	5.195%	$161.9687	$161.97	$161.95	$162.00
Purchase #6	$82.87	13.651%	$94.1826	$94.18	$94.20	$94.20
Purchase #7	$150.81	7.380%	$161.9398	$161.94	$161.95	$161.90
7 purchase totals =	$1,093.10		$1,196.3646	$1,196.37	$1,196.40	$1,196.50