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	$67.46	6.587%	$71.9036	$71.90	$71.90	$71.90
Purchase #2	$38.31	4.346%	$39.975	$39.98	$40.00	$40.00
Purchase #3	$18.97	13.313%	$21.4955	$21.50	$21.50	$21.50
Purchase #4	$48.32	10.847%	$53.5613	$53.56	$53.55	$53.60
Purchase #5	$188.86	3.690%	$195.8289	$195.83	$195.85	$195.80
Purchase #6	$149.27	5.833%	$157.9769	$157.98	$158.00	$158.00
Purchase #7	$169.69	6.709%	$181.0745	$181.07	$181.05	$181.10
7 purchase totals =	$680.88		$721.8157	$721.82	$721.85	$721.90