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	$117.97	8.343%	$127.8122	$127.81	$127.80	$127.80
Purchase #2	$237.44	10.110%	$261.4452	$261.45	$261.45	$261.40
Purchase #3	$130.99	9.136%	$142.9572	$142.96	$142.95	$143.00
Purchase #4	$202.49	11.195%	$225.1588	$225.16	$225.15	$225.20
Purchase #5	$127.59	10.765%	$141.3251	$141.33	$141.35	$141.30
Purchase #6	$86.90	3.707%	$90.1214	$90.12	$90.10	$90.10
Purchase #7	$145.91	10.648%	$161.4465	$161.45	$161.45	$161.40
7 purchase totals =	$1,049.29		$1,150.2664	$1,150.28	$1,150.25	$1,150.20