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	$50.44	8.615%	$54.7854	$54.79	$54.80	$54.80
Purchase #2	$21.78	7.391%	$23.3898	$23.39	$23.40	$23.40
Purchase #3	$65.55	9.617%	$71.8539	$71.85	$71.85	$71.90
Purchase #4	$98.90	5.824%	$104.6599	$104.66	$104.65	$104.70
Purchase #5	$94.86	4.799%	$99.4123	$99.41	$99.40	$99.40
Purchase #6	$165.79	4.657%	$173.5108	$173.51	$173.50	$173.50
Purchase #7	$107.29	4.226%	$111.8241	$111.82	$111.80	$111.80
7 purchase totals =	$604.61		$639.4362	$639.43	$639.40	$639.50