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	$67.71	3.628%	$70.1665	$70.17	$70.15	$70.20
Purchase #2	$133.30	12.515%	$149.9825	$149.98	$150.00	$150.00
Purchase #3	$240.92	7.848%	$259.8274	$259.83	$259.85	$259.80
Purchase #4	$38.40	6.403%	$40.8588	$40.86	$40.85	$40.90
Purchase #5	$54.26	9.534%	$59.4331	$59.43	$59.45	$59.40
Purchase #6	$89.50	13.799%	$101.8501	$101.85	$101.85	$101.90
Purchase #7	$34.89	12.255%	$39.1658	$39.17	$39.15	$39.20
7 purchase totals =	$658.98		$721.2842	$721.29	$721.30	$721.40