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	$39.70	4.270%	$41.3952	$41.40	$41.40	$41.40
Purchase #2	$214.97	7.698%	$231.5184	$231.52	$231.50	$231.50
Purchase #3	$232.87	5.654%	$246.0365	$246.04	$246.05	$246.00
Purchase #4	$40.92	11.753%	$45.7293	$45.73	$45.75	$45.70
Purchase #5	$111.93	11.357%	$124.6419	$124.64	$124.65	$124.60
Purchase #6	$98.32	13.117%	$111.2166	$111.22	$111.20	$111.20
Purchase #7	$250.93	11.709%	$280.3114	$280.31	$280.30	$280.30
7 purchase totals =	$989.64		$1,080.8493	$1,080.86	$1,080.85	$1,080.70