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	$79.58	13.774%	$90.5413	$90.54	$90.55	$90.50
Purchase #2	$77.87	11.410%	$86.755	$86.76	$86.75	$86.80
Purchase #3	$222.69	7.366%	$239.0933	$239.09	$239.10	$239.10
Purchase #4	$210.26	4.193%	$219.0762	$219.08	$219.10	$219.10
Purchase #5	$90.65	5.451%	$95.5913	$95.59	$95.60	$95.60
Purchase #6	$59.78	12.800%	$67.4318	$67.43	$67.45	$67.40
Purchase #7	$11.37	7.547%	$12.2281	$12.23	$12.25	$12.20
7 purchase totals =	$752.20		$810.7170	$810.72	$810.80	$810.70