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	$239.56	12.815%	$270.2596	$270.26	$270.25	$270.30
Purchase #2	$121.98	8.750%	$132.6533	$132.65	$132.65	$132.70
Purchase #3	$138.69	3.484%	$143.522	$143.52	$143.50	$143.50
Purchase #4	$170.26	7.405%	$182.8678	$182.87	$182.85	$182.90
Purchase #5	$123.69	3.419%	$127.919	$127.92	$127.90	$127.90
Purchase #6	$71.56	9.340%	$78.2437	$78.24	$78.25	$78.20
Purchase #7	$87.92	10.236%	$96.9195	$96.92	$96.90	$96.90
7 purchase totals =	$953.66		$1,032.3849	$1,032.38	$1,032.30	$1,032.40