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	$81.28	3.174%	$83.8598	$83.86	$83.85	$83.90
Purchase #2	$11.75	10.787%	$13.0175	$13.02	$13.00	$13.00
Purchase #3	$127.77	3.597%	$132.3659	$132.37	$132.35	$132.40
Purchase #4	$96.25	4.408%	$100.4927	$100.49	$100.50	$100.50
Purchase #5	$168.96	5.282%	$177.8845	$177.88	$177.90	$177.90
Purchase #6	$13.51	10.496%	$14.928	$14.93	$14.95	$14.90
Purchase #7	$247.93	3.383%	$256.3175	$256.32	$256.30	$256.30
7 purchase totals =	$747.45		$778.8659	$778.87	$778.85	$778.90