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	$41.77	3.219%	$43.1146	$43.11	$43.10	$43.10
Purchase #2	$131.79	13.839%	$150.0284	$150.03	$150.05	$150.00
Purchase #3	$11.26	11.248%	$12.5265	$12.53	$12.55	$12.50
Purchase #4	$37.50	9.409%	$41.0284	$41.03	$41.05	$41.00
Purchase #5	$157.35	5.444%	$165.9161	$165.92	$165.90	$165.90
Purchase #6	$172.53	13.640%	$196.0631	$196.06	$196.05	$196.10
Purchase #7	$28.67	7.766%	$30.8965	$30.90	$30.90	$30.90
7 purchase totals =	$580.87		$639.5736	$639.58	$639.60	$639.50