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	$87.50	3.244%	$90.3385	$90.34	$90.35	$90.30
Purchase #2	$127.30	9.559%	$139.4686	$139.47	$139.45	$139.50
Purchase #3	$225.41	9.748%	$247.383	$247.38	$247.40	$247.40
Purchase #4	$148.64	4.754%	$155.7063	$155.71	$155.70	$155.70
Purchase #5	$38.71	13.871%	$44.0795	$44.08	$44.10	$44.10
Purchase #6	$80.64	10.222%	$88.883	$88.88	$88.90	$88.90
Purchase #7	$106.44	12.128%	$119.349	$119.35	$119.35	$119.30
7 purchase totals =	$814.64		$885.2079	$885.21	$885.25	$885.20