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	$100.73	8.186%	$108.9758	$108.98	$109.00	$109.00
Purchase #2	$148.38	9.342%	$162.2417	$162.24	$162.25	$162.20
Purchase #3	$33.80	8.323%	$36.6132	$36.61	$36.60	$36.60
Purchase #4	$202.43	9.309%	$221.2742	$221.27	$221.25	$221.30
Purchase #5	$46.89	11.229%	$52.1553	$52.16	$52.15	$52.20
Purchase #6	$41.62	5.485%	$43.9029	$43.90	$43.90	$43.90
Purchase #7	$168.25	13.377%	$190.7568	$190.76	$190.75	$190.80
7 purchase totals =	$742.10		$815.9199	$815.92	$815.90	$816.00