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	$34.83	10.152%	$38.3659	$38.37	$38.35	$38.40
Purchase #2	$93.81	9.674%	$102.8852	$102.89	$102.90	$102.90
Purchase #3	$57.51	13.624%	$65.3452	$65.35	$65.35	$65.30
Purchase #4	$123.86	13.464%	$140.5365	$140.54	$140.55	$140.50
Purchase #5	$109.80	8.596%	$119.2384	$119.24	$119.25	$119.20
Purchase #6	$43.98	6.526%	$46.8501	$46.85	$46.85	$46.90
Purchase #7	$194.48	5.850%	$205.8571	$205.86	$205.85	$205.90
7 purchase totals =	$658.27		$719.0784	$719.10	$719.10	$719.10