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	$5.49	13.332%	$6.2219	$6.22	$6.20	$6.20
Purchase #2	$244.67	4.458%	$255.5774	$255.58	$255.60	$255.60
Purchase #3	$202.63	10.420%	$223.744	$223.74	$223.75	$223.70
Purchase #4	$79.60	4.133%	$82.8899	$82.89	$82.90	$82.90
Purchase #5	$46.73	5.112%	$49.1188	$49.12	$49.10	$49.10
Purchase #6	$62.30	6.706%	$66.4778	$66.48	$66.50	$66.50
Purchase #7	$12.87	3.683%	$13.344	$13.34	$13.35	$13.30
7 purchase totals =	$654.29		$697.3738	$697.37	$697.40	$697.30