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	$101.99	9.618%	$111.7994	$111.80	$111.80	$111.80
Purchase #2	$208.46	12.452%	$234.4174	$234.42	$234.40	$234.40
Purchase #3	$177.79	7.172%	$190.5411	$190.54	$190.55	$190.50
Purchase #4	$135.84	10.661%	$150.3219	$150.32	$150.30	$150.30
Purchase #5	$25.79	10.695%	$28.5482	$28.55	$28.55	$28.50
Purchase #6	$52.25	7.494%	$56.1656	$56.17	$56.15	$56.20
Purchase #7	$198.53	13.265%	$224.865	$224.87	$224.85	$224.90
7 purchase totals =	$900.65		$996.6586	$996.67	$996.60	$996.60