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	$159.79	12.239%	$179.3467	$179.35	$179.35	$179.30
Purchase #2	$44.52	6.638%	$47.4752	$47.48	$47.50	$47.50
Purchase #3	$99.85	8.319%	$108.1565	$108.16	$108.15	$108.20
Purchase #4	$155.69	5.624%	$164.446	$164.45	$164.45	$164.40
Purchase #5	$39.81	12.670%	$44.8539	$44.85	$44.85	$44.90
Purchase #6	$237.81	11.181%	$264.3995	$264.40	$264.40	$264.40
Purchase #7	$58.30	13.798%	$66.3442	$66.34	$66.35	$66.30
7 purchase totals =	$795.77		$875.0220	$875.03	$875.05	$875.00