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	$135.61	10.724%	$150.1528	$150.15	$150.15	$150.20
Purchase #2	$62.34	6.560%	$66.4295	$66.43	$66.45	$66.40
Purchase #3	$77.50	8.773%	$84.2991	$84.30	$84.30	$84.30
Purchase #4	$87.32	13.874%	$99.4348	$99.43	$99.45	$99.40
Purchase #5	$210.87	5.165%	$221.7614	$221.76	$221.75	$221.80
Purchase #6	$26.29	4.781%	$27.5469	$27.55	$27.55	$27.50
Purchase #7	$119.94	9.686%	$131.5574	$131.56	$131.55	$131.60
7 purchase totals =	$719.87		$781.1819	$781.18	$781.20	$781.20