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	$167.86	10.535%	$185.5441	$185.54	$185.55	$185.50
Purchase #2	$150.35	6.671%	$160.3798	$160.38	$160.40	$160.40
Purchase #3	$235.36	6.782%	$251.3221	$251.32	$251.30	$251.30
Purchase #4	$8.25	4.466%	$8.6184	$8.62	$8.60	$8.60
Purchase #5	$95.90	4.574%	$100.2865	$100.29	$100.30	$100.30
Purchase #6	$236.41	3.851%	$245.5141	$245.51	$245.50	$245.50
Purchase #7	$31.47	10.739%	$34.8496	$34.85	$34.85	$34.80
7 purchase totals =	$925.60		$986.5146	$986.51	$986.50	$986.40