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	$88.84	12.625%	$100.0561	$100.06	$100.05	$100.10
Purchase #2	$87.58	3.131%	$90.3221	$90.32	$90.30	$90.30
Purchase #3	$232.95	13.695%	$264.8525	$264.85	$264.85	$264.90
Purchase #4	$138.73	4.177%	$144.5248	$144.52	$144.50	$144.50
Purchase #5	$200.95	3.794%	$208.574	$208.57	$208.55	$208.60
Purchase #6	$107.76	6.623%	$114.8969	$114.90	$114.90	$114.90
Purchase #7	$175.68	12.292%	$197.2746	$197.27	$197.25	$197.30
7 purchase totals =	$1,032.49		$1,120.5010	$1,120.49	$1,120.40	$1,120.60