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	$75.34	11.696%	$84.1518	$84.15	$84.15	$84.20
Purchase #2	$9.84	12.789%	$11.0984	$11.10	$11.10	$11.10
Purchase #3	$126.93	12.872%	$143.2684	$143.27	$143.25	$143.30
Purchase #4	$167.51	11.188%	$186.251	$186.25	$186.25	$186.30
Purchase #5	$72.83	12.772%	$82.1318	$82.13	$82.15	$82.10
Purchase #6	$111.93	10.689%	$123.8942	$123.89	$123.90	$123.90
Purchase #7	$152.67	7.835%	$164.6317	$164.63	$164.65	$164.60
7 purchase totals =	$717.05		$795.4273	$795.42	$795.45	$795.50