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	$160.48	6.767%	$171.3397	$171.34	$171.35	$171.30
Purchase #2	$53.91	8.535%	$58.5112	$58.51	$58.50	$58.50
Purchase #3	$26.59	9.288%	$29.0597	$29.06	$29.05	$29.10
Purchase #4	$38.26	13.523%	$43.4339	$43.43	$43.45	$43.40
Purchase #5	$39.72	10.627%	$43.941	$43.94	$43.95	$43.90
Purchase #6	$167.65	6.786%	$179.0267	$179.03	$179.05	$179.00
Purchase #7	$150.37	5.302%	$158.3426	$158.34	$158.35	$158.30
7 purchase totals =	$636.98		$683.6548	$683.65	$683.70	$683.50