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	$34.44	10.151%	$37.936	$37.94	$37.95	$37.90
Purchase #2	$42.96	6.671%	$45.8259	$45.83	$45.85	$45.80
Purchase #3	$164.93	4.578%	$172.4805	$172.48	$172.50	$172.50
Purchase #4	$54.37	6.333%	$57.8133	$57.81	$57.80	$57.80
Purchase #5	$121.49	10.153%	$133.8249	$133.82	$133.80	$133.80
Purchase #6	$138.95	5.582%	$146.7062	$146.71	$146.70	$146.70
Purchase #7	$79.80	8.427%	$86.5247	$86.52	$86.50	$86.50
7 purchase totals =	$636.94		$681.1115	$681.11	$681.10	$681.00