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	$41.82	9.637%	$45.8502	$45.85	$45.85	$45.90
Purchase #2	$10.97	10.301%	$12.1	$12.10	$12.10	$12.10
Purchase #3	$184.84	9.545%	$202.483	$202.48	$202.50	$202.50
Purchase #4	$116.83	5.704%	$123.494	$123.49	$123.50	$123.50
Purchase #5	$93.67	11.477%	$104.4205	$104.42	$104.40	$104.40
Purchase #6	$113.42	4.125%	$118.0986	$118.10	$118.10	$118.10
Purchase #7	$59.48	6.269%	$63.2088	$63.21	$63.20	$63.20
7 purchase totals =	$621.03		$669.6551	$669.65	$669.65	$669.70