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	$82.29	8.829%	$89.5554	$89.56	$89.55	$89.60
Purchase #2	$113.97	7.286%	$122.2739	$122.27	$122.25	$122.30
Purchase #3	$156.51	3.520%	$162.0192	$162.02	$162.00	$162.00
Purchase #4	$155.54	5.600%	$164.2502	$164.25	$164.25	$164.30
Purchase #5	$179.68	9.596%	$196.9221	$196.92	$196.90	$196.90
Purchase #6	$76.58	8.787%	$83.3091	$83.31	$83.30	$83.30
Purchase #7	$107.38	12.849%	$121.1773	$121.18	$121.20	$121.20
7 purchase totals =	$871.95		$939.5072	$939.51	$939.45	$939.60