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	$245.54	5.566%	$259.2068	$259.21	$259.20	$259.20
Purchase #2	$189.75	3.747%	$196.8599	$196.86	$196.85	$196.90
Purchase #3	$26.72	10.697%	$29.5782	$29.58	$29.60	$29.60
Purchase #4	$135.30	8.683%	$147.0481	$147.05	$147.05	$147.00
Purchase #5	$61.90	9.348%	$67.6864	$67.69	$67.70	$67.70
Purchase #6	$219.39	5.622%	$231.7241	$231.72	$231.70	$231.70
Purchase #7	$52.31	13.560%	$59.4032	$59.40	$59.40	$59.40
7 purchase totals =	$930.91		$991.5067	$991.51	$991.50	$991.50