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	$71.51	9.419%	$78.2455	$78.25	$78.25	$78.20
Purchase #2	$246.42	4.771%	$258.1767	$258.18	$258.20	$258.20
Purchase #3	$187.46	6.468%	$199.5849	$199.58	$199.60	$199.60
Purchase #4	$231.27	5.824%	$244.7392	$244.74	$244.75	$244.70
Purchase #5	$90.45	13.564%	$102.7186	$102.72	$102.70	$102.70
Purchase #6	$231.53	5.824%	$245.0143	$245.01	$245.00	$245.00
Purchase #7	$132.43	7.850%	$142.8258	$142.83	$142.85	$142.80
7 purchase totals =	$1,191.07		$1,271.3050	$1,271.31	$1,271.35	$1,271.20