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	$179.42	4.498%	$187.4903	$187.49	$187.50	$187.50
Purchase #2	$164.55	11.348%	$183.2231	$183.22	$183.20	$183.20
Purchase #3	$46.48	10.492%	$51.3567	$51.36	$51.35	$51.40
Purchase #4	$59.45	3.603%	$61.592	$61.59	$61.60	$61.60
Purchase #5	$37.94	6.443%	$40.3845	$40.38	$40.40	$40.40
Purchase #6	$129.60	7.633%	$139.4924	$139.49	$139.50	$139.50
Purchase #7	$6.40	6.627%	$6.8241	$6.82	$6.80	$6.80
7 purchase totals =	$623.84		$670.3631	$670.35	$670.35	$670.40