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	$61.73	7.526%	$66.3758	$66.38	$66.40	$66.40
Purchase #2	$238.88	5.446%	$251.8894	$251.89	$251.90	$251.90
Purchase #3	$163.52	6.691%	$174.4611	$174.46	$174.45	$174.50
Purchase #4	$153.65	8.321%	$166.4352	$166.44	$166.45	$166.40
Purchase #5	$92.42	8.636%	$100.4014	$100.40	$100.40	$100.40
Purchase #6	$87.72	9.690%	$96.2201	$96.22	$96.20	$96.20
Purchase #7	$222.84	8.809%	$242.47	$242.47	$242.45	$242.50
7 purchase totals =	$1,020.76		$1,098.2530	$1,098.26	$1,098.25	$1,098.30