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	$79.52	4.710%	$83.2654	$83.27	$83.25	$83.30
Purchase #2	$179.36	3.578%	$185.7775	$185.78	$185.80	$185.80
Purchase #3	$120.65	9.639%	$132.2795	$132.28	$132.30	$132.30
Purchase #4	$94.36	5.791%	$99.8244	$99.82	$99.80	$99.80
Purchase #5	$73.81	4.231%	$76.9329	$76.93	$76.95	$76.90
Purchase #6	$32.35	6.272%	$34.379	$34.38	$34.40	$34.40
Purchase #7	$88.61	10.442%	$97.8627	$97.86	$97.85	$97.90
7 purchase totals =	$668.66		$710.3214	$710.32	$710.35	$710.40