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	$137.82	12.838%	$155.5133	$155.51	$155.50	$155.50
Purchase #2	$42.43	6.873%	$45.3462	$45.35	$45.35	$45.30
Purchase #3	$35.40	7.474%	$38.0458	$38.05	$38.05	$38.00
Purchase #4	$39.69	5.597%	$41.9114	$41.91	$41.90	$41.90
Purchase #5	$13.96	13.702%	$15.8728	$15.87	$15.85	$15.90
Purchase #6	$156.59	3.871%	$162.6516	$162.65	$162.65	$162.70
Purchase #7	$117.93	6.462%	$125.5506	$125.55	$125.55	$125.60
7 purchase totals =	$543.82		$584.8917	$584.89	$584.85	$584.90