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	$144.61	6.416%	$153.8882	$153.89	$153.90	$153.90
Purchase #2	$47.63	4.167%	$49.6147	$49.61	$49.60	$49.60
Purchase #3	$141.92	3.788%	$147.2959	$147.30	$147.30	$147.30
Purchase #4	$59.82	8.526%	$64.9203	$64.92	$64.90	$64.90
Purchase #5	$46.49	7.512%	$49.9823	$49.98	$50.00	$50.00
Purchase #6	$33.43	10.172%	$36.8305	$36.83	$36.85	$36.80
Purchase #7	$82.49	5.303%	$86.8644	$86.86	$86.85	$86.90
7 purchase totals =	$556.39		$589.3963	$589.39	$589.40	$589.40