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	$19.58	10.409%	$21.6181	$21.62	$21.60	$21.60
Purchase #2	$155.51	13.748%	$176.8895	$176.89	$176.90	$176.90
Purchase #3	$141.73	10.735%	$156.9447	$156.94	$156.95	$156.90
Purchase #4	$35.82	5.274%	$37.7091	$37.71	$37.70	$37.70
Purchase #5	$127.82	11.104%	$142.0131	$142.01	$142.00	$142.00
Purchase #6	$204.49	9.529%	$223.9759	$223.98	$224.00	$224.00
Purchase #7	$29.36	6.226%	$31.188	$31.19	$31.20	$31.20
7 purchase totals =	$714.31		$790.3384	$790.34	$790.35	$790.30