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	$96.82	8.797%	$105.3373	$105.34	$105.35	$105.30
Purchase #2	$196.59	13.261%	$222.6598	$222.66	$222.65	$222.70
Purchase #3	$172.75	11.479%	$192.58	$192.58	$192.60	$192.60
Purchase #4	$200.47	6.638%	$213.7772	$213.78	$213.80	$213.80
Purchase #5	$112.95	9.304%	$123.4589	$123.46	$123.45	$123.50
Purchase #6	$30.67	5.368%	$32.3164	$32.32	$32.30	$32.30
Purchase #7	$89.81	12.494%	$101.0309	$101.03	$101.05	$101.00
7 purchase totals =	$900.06		$991.1605	$991.17	$991.20	$991.20