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	$136.83	13.392%	$155.1543	$155.15	$155.15	$155.20
Purchase #2	$19.80	6.415%	$21.0702	$21.07	$21.05	$21.10
Purchase #3	$196.71	9.281%	$214.9667	$214.97	$214.95	$215.00
Purchase #4	$122.61	8.166%	$132.6223	$132.62	$132.60	$132.60
Purchase #5	$212.50	4.172%	$221.3655	$221.37	$221.35	$221.40
Purchase #6	$105.90	13.690%	$120.3977	$120.40	$120.40	$120.40
Purchase #7	$102.59	10.104%	$112.9557	$112.96	$112.95	$113.00
7 purchase totals =	$896.94		$978.5324	$978.54	$978.45	$978.70