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	$74.28	8.827%	$80.8367	$80.84	$80.85	$80.80
Purchase #2	$196.53	7.317%	$210.9101	$210.91	$210.90	$210.90
Purchase #3	$145.53	5.736%	$153.8776	$153.88	$153.90	$153.90
Purchase #4	$242.99	5.168%	$255.5477	$255.55	$255.55	$255.50
Purchase #5	$93.89	11.217%	$104.4216	$104.42	$104.40	$104.40
Purchase #6	$237.94	10.487%	$262.8928	$262.89	$262.90	$262.90
Purchase #7	$244.64	6.872%	$261.4517	$261.45	$261.45	$261.50
7 purchase totals =	$1,235.80		$1,329.9382	$1,329.94	$1,329.95	$1,329.90