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	$161.83	12.764%	$182.486	$182.49	$182.50	$182.50
Purchase #2	$172.95	5.732%	$182.8635	$182.86	$182.85	$182.90
Purchase #3	$55.67	12.379%	$62.5614	$62.56	$62.55	$62.60
Purchase #4	$70.66	12.339%	$79.3787	$79.38	$79.40	$79.40
Purchase #5	$81.27	9.536%	$89.0199	$89.02	$89.00	$89.00
Purchase #6	$26.80	10.643%	$29.6523	$29.65	$29.65	$29.70
Purchase #7	$81.60	9.690%	$89.507	$89.51	$89.50	$89.50
7 purchase totals =	$650.78		$715.4688	$715.47	$715.45	$715.60