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	$93.47	6.292%	$99.3511	$99.35	$99.35	$99.40
Purchase #2	$120.76	13.867%	$137.5058	$137.51	$137.50	$137.50
Purchase #3	$168.59	11.714%	$188.3386	$188.34	$188.35	$188.30
Purchase #4	$169.87	12.393%	$190.922	$190.92	$190.90	$190.90
Purchase #5	$19.39	10.732%	$21.4709	$21.47	$21.45	$21.50
Purchase #6	$59.83	11.568%	$66.7511	$66.75	$66.75	$66.80
Purchase #7	$227.32	7.149%	$243.5711	$243.57	$243.55	$243.60
7 purchase totals =	$859.23		$947.9106	$947.91	$947.85	$948.00