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	$37.70	11.730%	$42.1222	$42.12	$42.10	$42.10
Purchase #2	$76.30	11.431%	$85.0219	$85.02	$85.00	$85.00
Purchase #3	$217.90	8.573%	$236.5806	$236.58	$236.60	$236.60
Purchase #4	$70.93	10.527%	$78.3968	$78.40	$78.40	$78.40
Purchase #5	$199.54	13.755%	$226.9867	$226.99	$227.00	$227.00
Purchase #6	$162.82	5.464%	$171.7165	$171.72	$171.70	$171.70
Purchase #7	$97.52	13.483%	$110.6686	$110.67	$110.65	$110.70
7 purchase totals =	$862.71		$951.4933	$951.50	$951.45	$951.50