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	$235.32	9.406%	$257.4542	$257.45	$257.45	$257.50
Purchase #2	$212.46	12.447%	$238.9049	$238.90	$238.90	$238.90
Purchase #3	$237.86	7.450%	$255.5806	$255.58	$255.60	$255.60
Purchase #4	$18.82	12.283%	$21.1317	$21.13	$21.15	$21.10
Purchase #5	$51.89	13.180%	$58.7291	$58.73	$58.75	$58.70
Purchase #6	$70.48	13.751%	$80.1717	$80.17	$80.15	$80.20
Purchase #7	$216.55	8.233%	$234.3786	$234.38	$234.40	$234.40
7 purchase totals =	$1,043.38		$1,146.3508	$1,146.34	$1,146.40	$1,146.40