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	$139.57	12.180%	$156.5696	$156.57	$156.55	$156.60
Purchase #2	$51.90	4.678%	$54.3279	$54.33	$54.35	$54.30
Purchase #3	$219.86	11.176%	$244.4316	$244.43	$244.45	$244.40
Purchase #4	$62.39	6.363%	$66.3599	$66.36	$66.35	$66.40
Purchase #5	$226.98	10.601%	$251.0421	$251.04	$251.05	$251.00
Purchase #6	$33.59	13.871%	$38.2493	$38.25	$38.25	$38.20
Purchase #7	$214.50	3.451%	$221.9024	$221.90	$221.90	$221.90
7 purchase totals =	$948.79		$1,032.8828	$1,032.88	$1,032.90	$1,032.80