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	$223.60	7.289%	$239.8982	$239.90	$239.90	$239.90
Purchase #2	$211.30	12.834%	$238.4182	$238.42	$238.40	$238.40
Purchase #3	$138.44	13.387%	$156.973	$156.97	$156.95	$157.00
Purchase #4	$64.94	3.422%	$67.1622	$67.16	$67.15	$67.20
Purchase #5	$90.72	8.405%	$98.345	$98.35	$98.35	$98.30
Purchase #6	$206.59	5.538%	$218.031	$218.03	$218.05	$218.00
Purchase #7	$57.82	3.376%	$59.772	$59.77	$59.75	$59.80
7 purchase totals =	$993.41		$1,078.5996	$1,078.60	$1,078.55	$1,078.60