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	$199.58	6.277%	$212.1076	$212.11	$212.10	$212.10
Purchase #2	$74.94	7.390%	$80.4781	$80.48	$80.50	$80.50
Purchase #3	$92.30	11.161%	$102.6016	$102.60	$102.60	$102.60
Purchase #4	$113.32	12.771%	$127.7921	$127.79	$127.80	$127.80
Purchase #5	$128.74	3.122%	$132.7593	$132.76	$132.75	$132.80
Purchase #6	$65.80	5.356%	$69.3242	$69.32	$69.30	$69.30
Purchase #7	$172.83	13.696%	$196.5008	$196.50	$196.50	$196.50
7 purchase totals =	$847.51		$921.5637	$921.56	$921.55	$921.60