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	$6.97	13.577%	$7.9163	$7.92	$7.90	$7.90
Purchase #2	$144.29	8.491%	$156.5417	$156.54	$156.55	$156.50
Purchase #3	$5.28	6.109%	$5.6026	$5.60	$5.60	$5.60
Purchase #4	$63.56	12.780%	$71.683	$71.68	$71.70	$71.70
Purchase #5	$119.27	3.772%	$123.7689	$123.77	$123.75	$123.80
Purchase #6	$11.32	12.717%	$12.7596	$12.76	$12.75	$12.80
Purchase #7	$192.46	10.865%	$213.3708	$213.37	$213.35	$213.40
7 purchase totals =	$543.15		$591.6429	$591.64	$591.60	$591.70