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	$146.36	12.859%	$165.1804	$165.18	$165.20	$165.20
Purchase #2	$87.66	3.336%	$90.5843	$90.58	$90.60	$90.60
Purchase #3	$19.82	4.444%	$20.7008	$20.70	$20.70	$20.70
Purchase #4	$102.53	11.482%	$114.3025	$114.30	$114.30	$114.30
Purchase #5	$239.96	4.182%	$249.9951	$250.00	$250.00	$250.00
Purchase #6	$208.85	6.368%	$222.1496	$222.15	$222.15	$222.10
Purchase #7	$93.53	9.795%	$102.6913	$102.69	$102.70	$102.70
7 purchase totals =	$898.71		$965.6040	$965.60	$965.65	$965.60