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	$84.82	6.652%	$90.4622	$90.46	$90.45	$90.50
Purchase #2	$43.25	10.331%	$47.7182	$47.72	$47.70	$47.70
Purchase #3	$154.66	8.371%	$167.6066	$167.61	$167.60	$167.60
Purchase #4	$53.32	8.334%	$57.7637	$57.76	$57.75	$57.80
Purchase #5	$13.92	10.794%	$15.4225	$15.42	$15.40	$15.40
Purchase #6	$31.64	6.127%	$33.5786	$33.58	$33.60	$33.60
Purchase #7	$219.32	11.548%	$244.6471	$244.65	$244.65	$244.60
7 purchase totals =	$600.93		$657.1989	$657.20	$657.15	$657.20