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	$104.59	13.288%	$118.4879	$118.49	$118.50	$118.50
Purchase #2	$146.77	10.341%	$161.9475	$161.95	$161.95	$161.90
Purchase #3	$31.43	3.736%	$32.6042	$32.60	$32.60	$32.60
Purchase #4	$6.92	3.493%	$7.1617	$7.16	$7.15	$7.20
Purchase #5	$156.86	9.230%	$171.3382	$171.34	$171.35	$171.30
Purchase #6	$38.60	4.233%	$40.2339	$40.23	$40.25	$40.20
Purchase #7	$78.36	9.658%	$85.928	$85.93	$85.95	$85.90
7 purchase totals =	$563.53		$617.7014	$617.70	$617.75	$617.60