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	$156.41	5.818%	$165.5099	$165.51	$165.50	$165.50
Purchase #2	$54.95	8.434%	$59.5845	$59.58	$59.60	$59.60
Purchase #3	$242.51	8.837%	$263.9406	$263.94	$263.95	$263.90
Purchase #4	$102.83	11.801%	$114.965	$114.97	$114.95	$115.00
Purchase #5	$147.55	12.380%	$165.8167	$165.82	$165.80	$165.80
Purchase #6	$226.82	12.525%	$255.2292	$255.23	$255.25	$255.20
Purchase #7	$244.51	8.233%	$264.6405	$264.64	$264.65	$264.60
7 purchase totals =	$1,175.58		$1,289.6864	$1,289.69	$1,289.70	$1,289.60