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	$68.72	4.636%	$71.9059	$71.91	$71.90	$71.90
Purchase #2	$157.64	3.224%	$162.7223	$162.72	$162.70	$162.70
Purchase #3	$135.96	5.514%	$143.4568	$143.46	$143.45	$143.50
Purchase #4	$138.79	11.252%	$154.4067	$154.41	$154.40	$154.40
Purchase #5	$213.54	5.780%	$225.8826	$225.88	$225.90	$225.90
Purchase #6	$35.73	12.854%	$40.3227	$40.32	$40.30	$40.30
Purchase #7	$212.26	9.273%	$231.9429	$231.94	$231.95	$231.90
7 purchase totals =	$962.64		$1,030.6399	$1,030.64	$1,030.60	$1,030.60