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	$176.33	5.574%	$186.1586	$186.16	$186.15	$186.20
Purchase #2	$204.29	6.853%	$218.29	$218.29	$218.30	$218.30
Purchase #3	$97.54	6.111%	$103.5007	$103.50	$103.50	$103.50
Purchase #4	$28.99	10.800%	$32.1209	$32.12	$32.10	$32.10
Purchase #5	$34.37	3.296%	$35.5028	$35.50	$35.50	$35.50
Purchase #6	$33.84	4.531%	$35.3733	$35.37	$35.35	$35.40
Purchase #7	$49.71	7.666%	$53.5208	$53.52	$53.50	$53.50
7 purchase totals =	$625.07		$664.4671	$664.46	$664.40	$664.50