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	$156.48	13.323%	$177.3278	$177.33	$177.35	$177.30
Purchase #2	$49.43	5.472%	$52.1348	$52.13	$52.15	$52.10
Purchase #3	$133.62	13.670%	$151.8859	$151.89	$151.90	$151.90
Purchase #4	$12.38	8.766%	$13.4652	$13.47	$13.45	$13.50
Purchase #5	$91.42	13.720%	$103.9628	$103.96	$103.95	$104.00
Purchase #6	$142.83	6.569%	$152.2125	$152.21	$152.20	$152.20
Purchase #7	$174.46	3.703%	$180.9203	$180.92	$180.90	$180.90
7 purchase totals =	$760.62		$831.9093	$831.91	$831.90	$831.90