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	$24.31	6.475%	$25.8841	$25.88	$25.90	$25.90
Purchase #2	$250.51	6.265%	$266.2045	$266.20	$266.20	$266.20
Purchase #3	$98.76	12.459%	$111.0645	$111.06	$111.05	$111.10
Purchase #4	$213.57	9.166%	$233.1458	$233.15	$233.15	$233.10
Purchase #5	$31.92	7.588%	$34.3421	$34.34	$34.35	$34.30
Purchase #6	$47.70	12.833%	$53.8213	$53.82	$53.80	$53.80
Purchase #7	$214.29	13.105%	$242.3727	$242.37	$242.35	$242.40
7 purchase totals =	$881.06		$966.8350	$966.82	$966.80	$966.80