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	$198.94	13.692%	$226.1789	$226.18	$226.20	$226.20
Purchase #2	$116.38	3.843%	$120.8525	$120.85	$120.85	$120.90
Purchase #3	$178.73	3.728%	$185.3931	$185.39	$185.40	$185.40
Purchase #4	$210.74	9.535%	$230.8341	$230.83	$230.85	$230.80
Purchase #5	$152.95	12.509%	$172.0825	$172.08	$172.10	$172.10
Purchase #6	$106.37	3.816%	$110.4291	$110.43	$110.45	$110.40
Purchase #7	$94.61	5.423%	$99.7407	$99.74	$99.75	$99.70
7 purchase totals =	$1,058.72		$1,145.5109	$1,145.50	$1,145.60	$1,145.50