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	$242.67	13.167%	$274.6224	$274.62	$274.60	$274.60
Purchase #2	$40.95	8.824%	$44.5634	$44.56	$44.55	$44.60
Purchase #3	$23.98	12.582%	$26.9972	$27.00	$27.00	$27.00
Purchase #4	$13.70	13.289%	$15.5206	$15.52	$15.50	$15.50
Purchase #5	$245.82	4.179%	$256.0928	$256.09	$256.10	$256.10
Purchase #6	$152.98	12.821%	$172.5936	$172.59	$172.60	$172.60
Purchase #7	$63.86	6.167%	$67.7982	$67.80	$67.80	$67.80
7 purchase totals =	$783.96		$858.1882	$858.18	$858.15	$858.20