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	$97.36	6.229%	$103.4246	$103.42	$103.40	$103.40
Purchase #2	$90.57	11.639%	$101.1114	$101.11	$101.10	$101.10
Purchase #3	$62.30	4.852%	$65.3228	$65.32	$65.30	$65.30
Purchase #4	$154.39	8.144%	$166.9635	$166.96	$166.95	$167.00
Purchase #5	$237.69	12.222%	$266.7405	$266.74	$266.75	$266.70
Purchase #6	$75.36	9.385%	$82.4325	$82.43	$82.45	$82.40
Purchase #7	$215.96	13.530%	$245.1794	$245.18	$245.20	$245.20
7 purchase totals =	$933.63		$1,031.1747	$1,031.16	$1,031.15	$1,031.10