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	$79.77	7.193%	$85.5079	$85.51	$85.50	$85.50
Purchase #2	$117.30	8.552%	$127.3315	$127.33	$127.35	$127.30
Purchase #3	$184.98	10.732%	$204.8321	$204.83	$204.85	$204.80
Purchase #4	$89.89	4.491%	$93.927	$93.93	$93.95	$93.90
Purchase #5	$56.49	10.309%	$62.3136	$62.31	$62.30	$62.30
Purchase #6	$117.37	8.102%	$126.8793	$126.88	$126.90	$126.90
Purchase #7	$39.69	4.777%	$41.586	$41.59	$41.60	$41.60
7 purchase totals =	$685.49		$742.3774	$742.38	$742.45	$742.30