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	$81.30	9.753%	$89.2292	$89.23	$89.25	$89.20
Purchase #2	$231.59	8.752%	$251.8588	$251.86	$251.85	$251.90
Purchase #3	$18.61	13.582%	$21.1376	$21.14	$21.15	$21.10
Purchase #4	$126.61	3.581%	$131.1439	$131.14	$131.15	$131.10
Purchase #5	$155.87	9.698%	$170.9863	$170.99	$171.00	$171.00
Purchase #6	$229.64	13.812%	$261.3579	$261.36	$261.35	$261.40
Purchase #7	$105.44	5.357%	$111.0884	$111.09	$111.10	$111.10
7 purchase totals =	$949.06		$1,036.8021	$1,036.81	$1,036.85	$1,036.80