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	$130.98	10.397%	$144.598	$144.60	$144.60	$144.60
Purchase #2	$25.57	11.676%	$28.5556	$28.56	$28.55	$28.60
Purchase #3	$35.97	11.370%	$40.0598	$40.06	$40.05	$40.10
Purchase #4	$114.71	6.270%	$121.9023	$121.90	$121.90	$121.90
Purchase #5	$202.72	12.761%	$228.5891	$228.59	$228.60	$228.60
Purchase #6	$48.71	12.660%	$54.8767	$54.88	$54.90	$54.90
Purchase #7	$41.35	13.434%	$46.905	$46.91	$46.90	$46.90
7 purchase totals =	$600.01		$665.4865	$665.50	$665.50	$665.60