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	$99.97	13.140%	$113.1061	$113.11	$113.10	$113.10
Purchase #2	$125.39	12.189%	$140.6738	$140.67	$140.65	$140.70
Purchase #3	$90.94	12.555%	$102.3575	$102.36	$102.35	$102.40
Purchase #4	$219.96	13.671%	$250.0307	$250.03	$250.05	$250.00
Purchase #5	$68.69	12.828%	$77.5016	$77.50	$77.50	$77.50
Purchase #6	$27.52	8.361%	$29.8209	$29.82	$29.80	$29.80
Purchase #7	$79.85	11.826%	$89.2931	$89.29	$89.30	$89.30
7 purchase totals =	$712.32		$802.7837	$802.78	$802.75	$802.80