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	$79.38	13.855%	$90.3781	$90.38	$90.40	$90.40
Purchase #2	$70.31	12.311%	$78.9659	$78.97	$78.95	$79.00
Purchase #3	$41.54	7.791%	$44.7764	$44.78	$44.80	$44.80
Purchase #4	$52.83	8.853%	$57.507	$57.51	$57.50	$57.50
Purchase #5	$148.48	10.341%	$163.8343	$163.83	$163.85	$163.80
Purchase #6	$90.94	8.292%	$98.4807	$98.48	$98.50	$98.50
Purchase #7	$61.59	3.687%	$63.8608	$63.86	$63.85	$63.90
7 purchase totals =	$545.07		$597.8032	$597.81	$597.85	$597.90