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	$215.87	12.263%	$242.3421	$242.34	$242.35	$242.30
Purchase #2	$69.65	12.730%	$78.5164	$78.52	$78.50	$78.50
Purchase #3	$25.69	9.540%	$28.1408	$28.14	$28.15	$28.10
Purchase #4	$164.37	13.687%	$186.8673	$186.87	$186.85	$186.90
Purchase #5	$226.40	3.824%	$235.0575	$235.06	$235.05	$235.10
Purchase #6	$146.58	12.308%	$164.6211	$164.62	$164.60	$164.60
Purchase #7	$162.56	7.311%	$174.4448	$174.44	$174.45	$174.40
7 purchase totals =	$1,011.12		$1,109.9900	$1,109.99	$1,109.95	$1,109.90