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	$29.70	10.160%	$32.7175	$32.72	$32.70	$32.70
Purchase #2	$115.79	10.166%	$127.5612	$127.56	$127.55	$127.60
Purchase #3	$15.48	10.855%	$17.1604	$17.16	$17.15	$17.20
Purchase #4	$35.92	4.199%	$37.4283	$37.43	$37.45	$37.40
Purchase #5	$33.88	5.394%	$35.7075	$35.71	$35.70	$35.70
Purchase #6	$71.41	10.523%	$78.9245	$78.92	$78.90	$78.90
Purchase #7	$183.64	7.245%	$196.9447	$196.94	$196.95	$196.90
7 purchase totals =	$485.82		$526.4441	$526.44	$526.40	$526.40