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	$25.90	11.450%	$28.8656	$28.87	$28.85	$28.90
Purchase #2	$145.36	12.318%	$163.2654	$163.27	$163.25	$163.30
Purchase #3	$94.49	6.392%	$100.5298	$100.53	$100.55	$100.50
Purchase #4	$145.67	3.289%	$150.4611	$150.46	$150.45	$150.50
Purchase #5	$34.73	11.706%	$38.7955	$38.80	$38.80	$38.80
Purchase #6	$173.94	8.224%	$188.2448	$188.24	$188.25	$188.20
Purchase #7	$82.51	4.680%	$86.3715	$86.37	$86.35	$86.40
7 purchase totals =	$702.60		$756.5337	$756.54	$756.50	$756.60