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	$78.75	9.528%	$86.2533	$86.25	$86.25	$86.30
Purchase #2	$144.74	13.248%	$163.9152	$163.92	$163.90	$163.90
Purchase #3	$136.82	8.475%	$148.4155	$148.42	$148.40	$148.40
Purchase #4	$28.27	10.529%	$31.2465	$31.25	$31.25	$31.20
Purchase #5	$36.81	12.495%	$41.4094	$41.41	$41.40	$41.40
Purchase #6	$228.89	7.688%	$246.4871	$246.49	$246.50	$246.50
Purchase #7	$70.43	3.443%	$72.8549	$72.85	$72.85	$72.90
7 purchase totals =	$724.71		$790.5819	$790.59	$790.55	$790.60