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	$129.59	11.389%	$144.349	$144.35	$144.35	$144.30
Purchase #2	$33.44	9.152%	$36.5004	$36.50	$36.50	$36.50
Purchase #3	$144.28	13.297%	$163.4649	$163.46	$163.45	$163.50
Purchase #4	$189.89	9.711%	$208.3302	$208.33	$208.35	$208.30
Purchase #5	$81.27	12.237%	$91.215	$91.22	$91.20	$91.20
Purchase #6	$128.52	11.659%	$143.5041	$143.50	$143.50	$143.50
Purchase #7	$123.37	3.821%	$128.084	$128.08	$128.10	$128.10
7 purchase totals =	$830.36		$915.4476	$915.44	$915.45	$915.40