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	$123.81	11.401%	$137.9256	$137.93	$137.95	$137.90
Purchase #2	$124.27	11.286%	$138.2951	$138.30	$138.30	$138.30
Purchase #3	$10.76	10.849%	$11.9274	$11.93	$11.95	$11.90
Purchase #4	$110.83	4.187%	$115.4705	$115.47	$115.45	$115.50
Purchase #5	$82.31	13.637%	$93.5346	$93.53	$93.55	$93.50
Purchase #6	$167.88	6.646%	$179.0373	$179.04	$179.05	$179.00
Purchase #7	$176.64	11.456%	$196.8759	$196.88	$196.90	$196.90
7 purchase totals =	$796.50		$873.0664	$873.08	$873.15	$873.00