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	$40.31	5.209%	$42.4097	$42.41	$42.40	$42.40
Purchase #2	$139.65	6.350%	$148.5178	$148.52	$148.50	$148.50
Purchase #3	$142.77	12.416%	$160.4963	$160.50	$160.50	$160.50
Purchase #4	$13.64	5.580%	$14.4011	$14.40	$14.40	$14.40
Purchase #5	$81.70	8.861%	$88.9394	$88.94	$88.95	$88.90
Purchase #6	$48.31	7.766%	$52.0618	$52.06	$52.05	$52.10
Purchase #7	$197.32	13.366%	$223.6938	$223.69	$223.70	$223.70
7 purchase totals =	$663.70		$730.5199	$730.52	$730.50	$730.50