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	$75.63	8.832%	$82.3096	$82.31	$82.30	$82.30
Purchase #2	$140.53	12.392%	$157.9445	$157.94	$157.95	$157.90
Purchase #3	$70.70	3.153%	$72.9292	$72.93	$72.95	$72.90
Purchase #4	$175.89	5.184%	$185.0081	$185.01	$185.00	$185.00
Purchase #5	$46.40	11.801%	$51.8757	$51.88	$51.90	$51.90
Purchase #6	$238.55	5.599%	$251.9064	$251.91	$251.90	$251.90
Purchase #7	$89.32	8.812%	$97.1909	$97.19	$97.20	$97.20
7 purchase totals =	$837.02		$899.1644	$899.17	$899.20	$899.10