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	$243.86	12.395%	$274.0864	$274.09	$274.10	$274.10
Purchase #2	$121.72	9.772%	$133.6145	$133.61	$133.60	$133.60
Purchase #3	$29.91	10.461%	$33.0389	$33.04	$33.05	$33.00
Purchase #4	$117.94	4.580%	$123.3417	$123.34	$123.35	$123.30
Purchase #5	$78.70	5.201%	$82.7932	$82.79	$82.80	$82.80
Purchase #6	$159.35	3.411%	$164.7854	$164.79	$164.80	$164.80
Purchase #7	$95.74	9.577%	$104.909	$104.91	$104.90	$104.90
7 purchase totals =	$847.22		$916.5691	$916.57	$916.60	$916.50