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	$49.71	6.408%	$52.8954	$52.90	$52.90	$52.90
Purchase #2	$109.98	12.179%	$123.3745	$123.37	$123.35	$123.40
Purchase #3	$153.30	8.732%	$166.6862	$166.69	$166.70	$166.70
Purchase #4	$87.99	5.592%	$92.9104	$92.91	$92.90	$92.90
Purchase #5	$219.43	6.228%	$233.0961	$233.10	$233.10	$233.10
Purchase #6	$109.86	6.476%	$116.9745	$116.97	$116.95	$117.00
Purchase #7	$220.35	11.325%	$245.3046	$245.30	$245.30	$245.30
7 purchase totals =	$950.62		$1,031.2417	$1,031.24	$1,031.20	$1,031.30