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	$231.94	13.158%	$262.4587	$262.46	$262.45	$262.50
Purchase #2	$247.43	9.735%	$271.5173	$271.52	$271.50	$271.50
Purchase #3	$36.59	11.856%	$40.9281	$40.93	$40.95	$40.90
Purchase #4	$18.64	9.848%	$20.4757	$20.48	$20.50	$20.50
Purchase #5	$211.56	4.686%	$221.4737	$221.47	$221.45	$221.50
Purchase #6	$192.44	10.713%	$213.0561	$213.06	$213.05	$213.10
Purchase #7	$62.40	12.548%	$70.23	$70.23	$70.25	$70.20
7 purchase totals =	$1,001.00		$1,100.1396	$1,100.15	$1,100.15	$1,100.20