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	$229.90	4.648%	$240.5858	$240.59	$240.60	$240.60
Purchase #2	$210.29	12.635%	$236.8601	$236.86	$236.85	$236.90
Purchase #3	$28.50	3.615%	$29.5303	$29.53	$29.55	$29.50
Purchase #4	$24.43	11.442%	$27.2253	$27.23	$27.25	$27.20
Purchase #5	$32.71	3.115%	$33.7289	$33.73	$33.75	$33.70
Purchase #6	$16.90	7.306%	$18.1347	$18.13	$18.15	$18.10
Purchase #7	$127.78	12.652%	$143.9467	$143.95	$143.95	$143.90
7 purchase totals =	$670.51		$730.0118	$730.02	$730.10	$729.90