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	$138.92	12.678%	$156.5323	$156.53	$156.55	$156.50
Purchase #2	$44.46	11.468%	$49.5587	$49.56	$49.55	$49.60
Purchase #3	$174.47	9.820%	$191.603	$191.60	$191.60	$191.60
Purchase #4	$30.68	5.493%	$32.3653	$32.37	$32.35	$32.40
Purchase #5	$95.85	3.131%	$98.8511	$98.85	$98.85	$98.90
Purchase #6	$55.67	7.484%	$59.8363	$59.84	$59.85	$59.80
Purchase #7	$136.36	12.300%	$153.1323	$153.13	$153.15	$153.10
7 purchase totals =	$676.41		$741.8790	$741.88	$741.90	$741.90