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	$113.35	5.286%	$119.3417	$119.34	$119.35	$119.30
Purchase #2	$68.64	12.710%	$77.3641	$77.36	$77.35	$77.40
Purchase #3	$139.58	12.137%	$156.5208	$156.52	$156.50	$156.50
Purchase #4	$36.61	11.527%	$40.83	$40.83	$40.85	$40.80
Purchase #5	$30.60	6.126%	$32.4746	$32.47	$32.45	$32.50
Purchase #6	$104.63	11.433%	$116.5923	$116.59	$116.60	$116.60
Purchase #7	$25.97	7.519%	$27.9227	$27.92	$27.90	$27.90
7 purchase totals =	$519.38		$571.0462	$571.03	$571.00	$571.00