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	$29.61	7.744%	$31.903	$31.90	$31.90	$31.90
Purchase #2	$107.29	9.556%	$117.5426	$117.54	$117.55	$117.50
Purchase #3	$183.42	5.673%	$193.8254	$193.83	$193.85	$193.80
Purchase #4	$216.79	11.862%	$242.5056	$242.51	$242.50	$242.50
Purchase #5	$137.84	3.537%	$142.7154	$142.72	$142.70	$142.70
Purchase #6	$188.68	4.377%	$196.9385	$196.94	$196.95	$196.90
Purchase #7	$159.40	13.558%	$181.0115	$181.01	$181.00	$181.00
7 purchase totals =	$1,023.03		$1,106.4420	$1,106.45	$1,106.45	$1,106.30