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	$136.39	7.487%	$146.6015	$146.60	$146.60	$146.60
Purchase #2	$140.55	7.269%	$150.7666	$150.77	$150.75	$150.80
Purchase #3	$137.90	13.649%	$156.722	$156.72	$156.70	$156.70
Purchase #4	$147.87	3.327%	$152.7896	$152.79	$152.80	$152.80
Purchase #5	$96.64	11.820%	$108.0628	$108.06	$108.05	$108.10
Purchase #6	$220.68	10.143%	$243.0636	$243.06	$243.05	$243.10
Purchase #7	$166.58	4.150%	$173.4931	$173.49	$173.50	$173.50
7 purchase totals =	$1,046.61		$1,131.4992	$1,131.49	$1,131.45	$1,131.60