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	$6.77	6.811%	$7.2311	$7.23	$7.25	$7.20
Purchase #2	$165.82	4.259%	$172.8823	$172.88	$172.90	$172.90
Purchase #3	$32.63	7.696%	$35.1412	$35.14	$35.15	$35.10
Purchase #4	$196.39	11.297%	$218.5762	$218.58	$218.60	$218.60
Purchase #5	$76.94	8.676%	$83.6153	$83.62	$83.60	$83.60
Purchase #6	$22.64	4.251%	$23.6024	$23.60	$23.60	$23.60
Purchase #7	$16.88	3.408%	$17.4553	$17.46	$17.45	$17.50
7 purchase totals =	$518.07		$558.5038	$558.51	$558.55	$558.50