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	$24.80	10.351%	$27.367	$27.37	$27.35	$27.40
Purchase #2	$145.72	6.177%	$154.7211	$154.72	$154.70	$154.70
Purchase #3	$231.56	5.498%	$244.2912	$244.29	$244.30	$244.30
Purchase #4	$159.33	9.748%	$174.8615	$174.86	$174.85	$174.90
Purchase #5	$196.52	9.391%	$214.9752	$214.98	$215.00	$215.00
Purchase #6	$84.42	5.439%	$89.0116	$89.01	$89.00	$89.00
Purchase #7	$238.38	4.565%	$249.262	$249.26	$249.25	$249.30
7 purchase totals =	$1,080.73		$1,154.4896	$1,154.49	$1,154.45	$1,154.60