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	$221.94	7.842%	$239.3445	$239.34	$239.35	$239.30
Purchase #2	$210.64	5.639%	$222.518	$222.52	$222.50	$222.50
Purchase #3	$17.61	4.445%	$18.3928	$18.39	$18.40	$18.40
Purchase #4	$187.28	9.780%	$205.596	$205.60	$205.60	$205.60
Purchase #5	$150.30	12.739%	$169.4467	$169.45	$169.45	$169.40
Purchase #6	$18.79	3.429%	$19.4343	$19.43	$19.45	$19.40
Purchase #7	$137.80	3.325%	$142.3819	$142.38	$142.40	$142.40
7 purchase totals =	$944.36		$1,017.1142	$1,017.11	$1,017.15	$1,017.00