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	$36.96	10.714%	$40.9199	$40.92	$40.90	$40.90
Purchase #2	$156.59	5.277%	$164.8533	$164.85	$164.85	$164.90
Purchase #3	$28.33	13.680%	$32.2055	$32.21	$32.20	$32.20
Purchase #4	$10.30	5.591%	$10.8759	$10.88	$10.90	$10.90
Purchase #5	$138.94	5.168%	$146.1204	$146.12	$146.10	$146.10
Purchase #6	$41.80	11.127%	$46.4511	$46.45	$46.45	$46.50
Purchase #7	$56.96	3.442%	$58.9206	$58.92	$58.90	$58.90
7 purchase totals =	$469.88		$500.3467	$500.35	$500.30	$500.40