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	$143.47	9.156%	$156.6061	$156.61	$156.60	$156.60
Purchase #2	$138.87	11.544%	$154.9012	$154.90	$154.90	$154.90
Purchase #3	$247.50	6.333%	$263.1742	$263.17	$263.15	$263.20
Purchase #4	$79.33	9.820%	$87.1202	$87.12	$87.10	$87.10
Purchase #5	$85.92	5.229%	$90.4128	$90.41	$90.40	$90.40
Purchase #6	$230.91	11.121%	$256.5895	$256.59	$256.60	$256.60
Purchase #7	$116.62	12.328%	$130.9969	$131.00	$131.00	$131.00
7 purchase totals =	$1,042.62		$1,139.8009	$1,139.80	$1,139.75	$1,139.80