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	$130.31	8.123%	$140.8951	$140.90	$140.90	$140.90
Purchase #2	$164.43	13.113%	$185.9917	$185.99	$186.00	$186.00
Purchase #3	$131.66	8.709%	$143.1263	$143.13	$143.15	$143.10
Purchase #4	$162.82	8.658%	$176.917	$176.92	$176.90	$176.90
Purchase #5	$238.75	10.509%	$263.8402	$263.84	$263.85	$263.80
Purchase #6	$129.79	7.294%	$139.2569	$139.26	$139.25	$139.30
Purchase #7	$154.38	10.832%	$171.1024	$171.10	$171.10	$171.10
7 purchase totals =	$1,112.14		$1,221.1296	$1,221.14	$1,221.15	$1,221.10