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	$153.53	7.352%	$164.8175	$164.82	$164.80	$164.80
Purchase #2	$242.43	11.183%	$269.5409	$269.54	$269.55	$269.50
Purchase #3	$92.88	6.808%	$99.2033	$99.20	$99.20	$99.20
Purchase #4	$198.52	8.493%	$215.3803	$215.38	$215.40	$215.40
Purchase #5	$250.86	8.273%	$271.6136	$271.61	$271.60	$271.60
Purchase #6	$67.85	11.725%	$75.8054	$75.81	$75.80	$75.80
Purchase #7	$172.52	5.233%	$181.548	$181.55	$181.55	$181.50
7 purchase totals =	$1,178.59		$1,277.9090	$1,277.91	$1,277.90	$1,277.80