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	$87.61	3.111%	$90.3355	$90.34	$90.35	$90.30
Purchase #2	$38.92	3.814%	$40.4044	$40.40	$40.40	$40.40
Purchase #3	$183.32	4.163%	$190.9516	$190.95	$190.95	$191.00
Purchase #4	$168.46	11.727%	$188.2153	$188.22	$188.20	$188.20
Purchase #5	$86.40	13.190%	$97.7962	$97.80	$97.80	$97.80
Purchase #6	$96.47	8.330%	$104.506	$104.51	$104.50	$104.50
Purchase #7	$231.68	3.290%	$239.3023	$239.30	$239.30	$239.30
7 purchase totals =	$892.86		$951.5113	$951.52	$951.50	$951.50