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	$18.75	9.221%	$20.4789	$20.48	$20.50	$20.50
Purchase #2	$197.36	12.810%	$222.6418	$222.64	$222.65	$222.60
Purchase #3	$163.38	10.513%	$180.5561	$180.56	$180.55	$180.60
Purchase #4	$166.98	3.859%	$173.4238	$173.42	$173.40	$173.40
Purchase #5	$186.51	4.268%	$194.4702	$194.47	$194.45	$194.50
Purchase #6	$182.34	4.430%	$190.4177	$190.42	$190.40	$190.40
Purchase #7	$71.55	8.229%	$77.4378	$77.44	$77.45	$77.40
7 purchase totals =	$986.87		$1,059.4263	$1,059.43	$1,059.40	$1,059.40