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	$78.63	6.284%	$83.5711	$83.57	$83.55	$83.60
Purchase #2	$59.83	12.769%	$67.4697	$67.47	$67.45	$67.50
Purchase #3	$233.87	7.122%	$250.5262	$250.53	$250.55	$250.50
Purchase #4	$107.63	9.178%	$117.5083	$117.51	$117.50	$117.50
Purchase #5	$139.77	13.276%	$158.3259	$158.33	$158.35	$158.30
Purchase #6	$182.84	4.215%	$190.5467	$190.55	$190.55	$190.50
Purchase #7	$207.52	11.737%	$231.8766	$231.88	$231.90	$231.90
7 purchase totals =	$1,010.09		$1,099.8245	$1,099.84	$1,099.85	$1,099.80