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	$23.51	5.643%	$24.8367	$24.84	$24.85	$24.80
Purchase #2	$51.85	6.592%	$55.268	$55.27	$55.25	$55.30
Purchase #3	$97.62	9.136%	$106.5386	$106.54	$106.55	$106.50
Purchase #4	$115.64	13.547%	$131.3058	$131.31	$131.30	$131.30
Purchase #5	$25.48	6.676%	$27.181	$27.18	$27.20	$27.20
Purchase #6	$136.35	6.255%	$144.8787	$144.88	$144.90	$144.90
Purchase #7	$50.72	4.808%	$53.1586	$53.16	$53.15	$53.20
7 purchase totals =	$501.17		$543.1674	$543.18	$543.20	$543.20