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	$24.38	10.830%	$27.0204	$27.02	$27.00	$27.00
Purchase #2	$188.39	3.761%	$195.4753	$195.48	$195.50	$195.50
Purchase #3	$134.28	7.580%	$144.4584	$144.46	$144.45	$144.50
Purchase #4	$50.49	5.771%	$53.4038	$53.40	$53.40	$53.40
Purchase #5	$62.60	7.588%	$67.3501	$67.35	$67.35	$67.40
Purchase #6	$66.80	4.621%	$69.8868	$69.89	$69.90	$69.90
Purchase #7	$90.52	8.764%	$98.4532	$98.45	$98.45	$98.50
7 purchase totals =	$617.46		$656.0480	$656.05	$656.05	$656.20