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	$59.60	8.152%	$64.4586	$64.46	$64.45	$64.50
Purchase #2	$53.80	7.655%	$57.9184	$57.92	$57.90	$57.90
Purchase #3	$247.96	3.135%	$255.7335	$255.73	$255.75	$255.70
Purchase #4	$29.89	11.642%	$33.3698	$33.37	$33.35	$33.40
Purchase #5	$172.74	6.118%	$183.3082	$183.31	$183.30	$183.30
Purchase #6	$127.51	13.582%	$144.8284	$144.83	$144.85	$144.80
Purchase #7	$129.74	10.228%	$143.0098	$143.01	$143.00	$143.00
7 purchase totals =	$821.24		$882.6267	$882.63	$882.60	$882.60