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	$76.58	5.126%	$80.5055	$80.51	$80.50	$80.50
Purchase #2	$35.96	11.583%	$40.1252	$40.13	$40.15	$40.10
Purchase #3	$233.50	8.727%	$253.8775	$253.88	$253.90	$253.90
Purchase #4	$95.60	8.348%	$103.5807	$103.58	$103.60	$103.60
Purchase #5	$93.27	11.221%	$103.7358	$103.74	$103.75	$103.70
Purchase #6	$224.31	7.849%	$241.9161	$241.92	$241.90	$241.90
Purchase #7	$202.78	9.531%	$222.107	$222.11	$222.10	$222.10
7 purchase totals =	$962.00		$1,045.8478	$1,045.87	$1,045.90	$1,045.80