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	$136.54	6.281%	$145.1161	$145.12	$145.10	$145.10
Purchase #2	$37.86	10.577%	$41.8645	$41.86	$41.85	$41.90
Purchase #3	$182.82	7.671%	$196.8441	$196.84	$196.85	$196.80
Purchase #4	$150.30	8.491%	$163.062	$163.06	$163.05	$163.10
Purchase #5	$86.63	5.874%	$91.7186	$91.72	$91.70	$91.70
Purchase #6	$122.85	4.774%	$128.7149	$128.71	$128.70	$128.70
Purchase #7	$37.82	6.416%	$40.2465	$40.25	$40.25	$40.20
7 purchase totals =	$754.82		$807.5667	$807.56	$807.50	$807.50