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	$60.57	6.704%	$64.6306	$64.63	$64.65	$64.60
Purchase #2	$87.97	5.465%	$92.7776	$92.78	$92.80	$92.80
Purchase #3	$112.64	10.105%	$124.0223	$124.02	$124.00	$124.00
Purchase #4	$36.45	5.256%	$38.3658	$38.37	$38.35	$38.40
Purchase #5	$81.89	6.390%	$87.1228	$87.12	$87.10	$87.10
Purchase #6	$99.71	3.574%	$103.2736	$103.27	$103.25	$103.30
Purchase #7	$152.85	4.201%	$159.2712	$159.27	$159.25	$159.30
7 purchase totals =	$632.08		$669.4639	$669.46	$669.40	$669.50