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	$137.59	10.405%	$151.9062	$151.91	$151.90	$151.90
Purchase #2	$71.71	12.850%	$80.9247	$80.92	$80.90	$80.90
Purchase #3	$77.41	8.321%	$83.8513	$83.85	$83.85	$83.90
Purchase #4	$16.89	7.728%	$18.1953	$18.20	$18.20	$18.20
Purchase #5	$140.63	12.716%	$158.5125	$158.51	$158.50	$158.50
Purchase #6	$25.83	6.855%	$27.6006	$27.60	$27.60	$27.60
Purchase #7	$214.93	8.590%	$233.3925	$233.39	$233.40	$233.40
7 purchase totals =	$684.99		$754.3831	$754.38	$754.35	$754.40