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	$74.74	5.713%	$79.0099	$79.01	$79.00	$79.00
Purchase #2	$123.33	6.776%	$131.6868	$131.69	$131.70	$131.70
Purchase #3	$174.34	6.318%	$185.3548	$185.35	$185.35	$185.40
Purchase #4	$224.78	13.754%	$255.6962	$255.70	$255.70	$255.70
Purchase #5	$227.38	11.330%	$253.1422	$253.14	$253.15	$253.10
Purchase #6	$69.88	9.490%	$76.5116	$76.51	$76.50	$76.50
Purchase #7	$21.35	10.516%	$23.5952	$23.60	$23.60	$23.60
7 purchase totals =	$915.80		$1,004.9967	$1,005.00	$1,005.00	$1,005.00