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	$126.93	9.356%	$138.8056	$138.81	$138.80	$138.80
Purchase #2	$132.91	7.138%	$142.3971	$142.40	$142.40	$142.40
Purchase #3	$146.94	6.479%	$156.4602	$156.46	$156.45	$156.50
Purchase #4	$71.51	3.819%	$74.241	$74.24	$74.25	$74.20
Purchase #5	$83.88	9.132%	$91.5399	$91.54	$91.55	$91.50
Purchase #6	$31.72	5.762%	$33.5477	$33.55	$33.55	$33.50
Purchase #7	$150.77	10.689%	$166.8858	$166.89	$166.90	$166.90
7 purchase totals =	$744.66		$803.8773	$803.89	$803.90	$803.80