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	$18.31	12.452%	$20.59	$20.59	$20.60	$20.60
Purchase #2	$241.27	5.239%	$253.9101	$253.91	$253.90	$253.90
Purchase #3	$114.51	12.128%	$128.3978	$128.40	$128.40	$128.40
Purchase #4	$185.53	7.498%	$199.441	$199.44	$199.45	$199.40
Purchase #5	$199.32	9.569%	$218.3929	$218.39	$218.40	$218.40
Purchase #6	$158.47	10.322%	$174.8273	$174.83	$174.85	$174.80
Purchase #7	$60.55	12.155%	$67.9099	$67.91	$67.90	$67.90
7 purchase totals =	$977.96		$1,063.4690	$1,063.47	$1,063.50	$1,063.40